diff --git a/README.md b/README.md
index 67fd593f..ab4803b1 100644
--- a/README.md
+++ b/README.md
@@ -34,637 +34,642 @@
### Table of Contents
-| No. | Questions |
-| --- | --------- |
-| 1 | [What are the possible ways to create objects in JavaScript](#what-are-the-possible-ways-to-create-objects-in-javascript) |
-| 2 | [What is a prototype chain](#what-is-a-prototype-chain) |
-| 3 | [What is the Difference Between `call`, `apply`, and `bind`](#what-is-the-difference-between-call-apply-and-bind) |
-| 4 | [What is JSON and its common operations](#what-is-json-and-its-common-operations) |
-| 5 | [What is the purpose of the array slice method](#what-is-the-purpose-of-the-array-slice-method) |
-| 6 | [What is the purpose of the array splice method](#what-is-the-purpose-of-the-array-splice-method) |
-| 7 | [What is the difference between slice and splice](#what-is-the-difference-between-slice-and-splice) |
-| 8 | [How do you compare Object and Map](#how-do-you-compare-object-and-map) |
-| 9 | [What is the difference between == and === operators](#what-is-the-difference-between--and--operators) |
-| 10 | [What are lambda expressions or arrow functions](#what-are-lambda-expressions-or-arrow-functions) |
-| 11 | [What is a first class function](#what-is-a-first-class-function) |
-| 12 | [What is a first order function](#what-is-a-first-order-function) |
-| 13 | [What is a higher order function](#what-is-a-higher-order-function) |
-| 14 | [What is a unary function](#what-is-a-unary-function) |
-| 15 | [What is the currying function](#what-is-the-currying-function) |
-| 16 | [What is a pure function](#what-is-a-pure-function) |
-| 17 | [What are the benefits of pure functions](#what-are-the-benefits-of-pure-functions) |
-| 18 | [What is the purpose of the let keyword](#what-is-the-purpose-of-the-let-keyword) |
-| 19 | [What is the difference between let and var](#what-is-the-difference-between-let-and-var) |
-| 20 | [What is the reason to choose the name let as a keyword](#what-is-the-reason-to-choose-the-name-let-as-a-keyword) |
-| 21 | [How do you redeclare variables in a switch block without an error](#how-do-you-redeclare-variables-in-a-switch-block-without-an-error) |
-| 22 | [What is the Temporal Dead Zone](#what-is-the-temporal-dead-zone) |
-| 23 | [What is an IIFE (Immediately Invoked Function Expression)](#what-is-an-iife-immediately-invoked-function-expression) |
-| 24 | [How do you decode or encode a URL in JavaScript?](#how-do-you-decode-or-encode-a-url-in-javascript) |
-| 25 | [What is memoization](#what-is-memoization) |
-| 26 | [What is Hoisting](#what-is-hoisting) |
-| 27 | [What are classes in ES6](#what-are-classes-in-es6) |
-| 28 | [What are closures](#what-are-closures) |
-| 29 | [What are modules](#what-are-modules) |
-| 30 | [Why do you need modules](#why-do-you-need-modules) |
-| 31 | [What is scope in javascript](#what-is-scope-in-javascript) |
-| 32 | [What is a service worker](#what-is-a-service-worker) |
-| 33 | [How do you manipulate DOM using a service worker](#how-do-you-manipulate-dom-using-a-service-worker) |
-| 34 | [How do you reuse information across service worker restarts](#how-do-you-reuse-information-across-service-worker-restarts) |
-| 35 | [What is IndexedDB](#what-is-indexeddb) |
-| 36 | [What is web storage](#what-is-web-storage) |
-| 37 | [What is a post message](#what-is-a-post-message) |
-| 38 | [What is a Cookie](#what-is-a-cookie) |
-| 39 | [Why do you need a Cookie](#why-do-you-need-a-cookie) |
-| 40 | [What are the options in a cookie](#what-are-the-options-in-a-cookie) |
-| 41 | [How do you delete a cookie](#how-do-you-delete-a-cookie) |
-| 42 | [What are the differences between cookie, local storage and session storage](#what-are-the-differences-between-cookie-local-storage-and-session-storage) |
-| 43 | [What is the main difference between localStorage and sessionStorage](#what-is-the-main-difference-between-localstorage-and-sessionstorage) |
-| 44 | [How do you access web storage](#how-do-you-access-web-storage) |
-| 45 | [What are the methods available on session storage](#what-are-the-methods-available-on-session-storage) |
-| 46 | [What is a storage event and its event handler](#what-is-a-storage-event-and-its-event-handler) |
-| 47 | [Why do you need web storage](#why-do-you-need-web-storage) |
-| 48 | [How do you check web storage browser support](#how-do-you-check-web-storage-browser-support) |
-| 49 | [How do you check web workers browser support](#how-do-you-check-web-workers-browser-support) |
-| 50 | [Give an example of a web worker](#give-an-example-of-a-web-worker) |
-| 51 | [What are the restrictions of web workers on DOM](#what-are-the-restrictions-of-web-workers-on-dom) |
-| 52 | [What is a promise](#what-is-a-promise) |
-| 53 | [Why do you need a promise](#why-do-you-need-a-promise) |
-| 54 | [Explain the three states of promise](#explain-the-three-states-of-promise) |
-| 55 | [What is a callback function](#what-is-a-callback-function) |
-| 56 | [Why do we need callbacks](#why-do-we-need-callbacks) |
-| 57 | [What is a callback hell](#what-is-a-callback-hell) |
-| 58 | [What are server-sent events](#what-are-server-sent-events) |
-| 59 | [How do you receive server-sent event notifications](#how-do-you-receive-server-sent-event-notifications) |
-| 60 | [How do you check browser support for server-sent events](#how-do-you-check-browser-support-for-server-sent-events) |
-| 61 | [What are the events available for server sent events](#what-are-the-events-available-for-server-sent-events) |
-| 62 | [What are the main rules of promise](#what-are-the-main-rules-of-promise) |
-| 63 | [What is callback in callback](#what-is-callback-in-callback) |
-| 64 | [What is promise chaining](#what-is-promise-chaining) |
-| 65 | [What is promise.all](#what-is-promiseall) |
-| 66 | [What is the purpose of the race method in promise](#what-is-the-purpose-of-the-race-method-in-promise) |
-| 67 | [What is a strict mode in javascript](#what-is-a-strict-mode-in-javascript) |
-| 68 | [Why do you need strict mode](#why-do-you-need-strict-mode) |
-| 69 | [How do you declare strict mode](#how-do-you-declare-strict-mode) |
-| 70 | [What is the purpose of double exclamation](#what-is-the-purpose-of-double-exclamation) |
-| 71 | [What is the purpose of the delete operator](#what-is-the-purpose-of-the-delete-operator) |
-| 72 | [What is typeof operator](#what-is-typeof-operator) |
-| 73 | [What is undefined property](#what-is-undefined-property) |
-| 74 | [What is null value](#what-is-null-value) |
-| 75 | [What is the difference between null and undefined](#what-is-the-difference-between-null-and-undefined) |
-| 76 | [What is eval](#what-is-eval) |
-| 77 | [What is the difference between window and document](#what-is-the-difference-between-window-and-document) |
-| 78 | [How do you access history in javascript](#how-do-you-access-history-in-javascript) |
-| 79 | [How do you detect caps lock key turned on or not](#how-do-you-detect-caps-lock-key-turned-on-or-not) |
-| 80 | [What is isNaN](#what-is-isnan) |
-| 81 | [What are the differences between undeclared and undefined variables](#what-are-the-differences-between-undeclared-and-undefined-variables) |
-| 82 | [What are global variables](#what-are-global-variables) |
-| 83 | [What are the problems with global variables](#what-are-the-problems-with-global-variables) |
-| 84 | [What is NaN property](#what-is-nan-property) |
-| 85 | [What is the purpose of isFinite function](#what-is-the-purpose-of-isfinite-function) |
-| 86 | [What is an event flow](#what-is-an-event-flow) |
-| 87 | [What is event capturing](#what-is-event-capturing) |
-| 88 | [What is event bubbling](#what-is-event-bubbling) |
-| 89 | [How do you submit a form using JavaScript](#how-do-you-submit-a-form-using-javascript) |
-| 90 | [How do you find operating system details](#how-do-you-find-operating-system-details) |
-| 91 | [What is the difference between document load and DOMContentLoaded events](#what-is-the-difference-between-document-load-and-domcontentloaded-events) |
-| 92 | [What is the difference between native, host and user objects](#what-is-the-difference-between-native-host-and-user-objects) |
-| 93 | [What are the tools or techniques used for debugging JavaScript code](#what-are-the-tools-or-techniques-used-for-debugging-javascript-code) |
-| 94 | [What are the pros and cons of promises over callbacks](#what-are-the-pros-and-cons-of-promises-over-callbacks) |
-| 95 | [What is the difference between an attribute and a property](#what-is-the-difference-between-an-attribute-and-a-property) |
-| 96 | [What is same-origin policy](#what-is-same-origin-policy) |
-| 97 | [What is the purpose of void 0](#what-is-the-purpose-of-void-0) |
-| 98 | [Is JavaScript a compiled or interpreted language](#is-javascript-a-compiled-or-interpreted-language) |
-| 99 | [Is JavaScript a case-sensitive language](#is-javascript-a-case-sensitive-language) |
-| 100 | [Is there any relation between Java and JavaScript](#is-there-any-relation-between-java-and-javascript) |
-| 101 | [What are events](#what-are-events) |
-| 102 | [Who created javascript](#who-created-javascript) |
-| 103 | [What is the use of preventDefault method](#what-is-the-use-of-preventdefault-method) |
-| 104 | [What is the use of stopPropagation method](#what-is-the-use-of-stoppropagation-method) |
-| 105 | [What are the steps involved in return false usage](#what-are-the-steps-involved-in-return-false-usage) |
-| 106 | [What is BOM](#what-is-bom) |
-| 107 | [What is the use of setTimeout](#what-is-the-use-of-settimeout) |
-| 108 | [What is the use of setInterval](#what-is-the-use-of-setinterval) |
-| 109 | [Why is JavaScript treated as Single threaded](#why-is-javascript-treated-as-single-threaded) |
-| 110 | [What is an event delegation](#what-is-an-event-delegation) |
-| 111 | [What is ECMAScript](#what-is-ecmascript) |
-| 112 | [What is JSON](#what-is-json) |
-| 113 | [What are the syntax rules of JSON](#what-are-the-syntax-rules-of-json) |
-| 114 | [What is the purpose JSON stringify](#what-is-the-purpose-json-stringify) |
-| 115 | [How do you parse JSON string](#how-do-you-parse-json-string) |
-| 116 | [Why do you need JSON](#why-do-you-need-json) |
-| 117 | [What are PWAs](#what-are-pwas) |
-| 118 | [What is the purpose of clearTimeout method](#what-is-the-purpose-of-cleartimeout-method) |
-| 119 | [What is the purpose of clearInterval method](#what-is-the-purpose-of-clearinterval-method) |
-| 120 | [How do you redirect new page in javascript](#how-do-you-redirect-new-page-in-javascript) |
-| 121 | [How do you check whether a string contains a substring](#how-do-you-check-whether-a-string-contains-a-substring) |
-| 122 | [How do you validate an email in javascript](#how-do-you-validate-an-email-in-javascript) |
-| 123 | [How do you get the current url with javascript](#how-do-you-get-the-current-url-with-javascript) |
-| 124 | [What are the various url properties of location object](#what-are-the-various-url-properties-of-location-object) |
-| 125 | [How do get query string values in javascript](#how-do-get-query-string-values-in-javascript) |
-| 126 | [How do you check if a key exists in an object](#how-do-you-check-if-a-key-exists-in-an-object) |
-| 127 | [How do you loop through or enumerate javascript object](#how-do-you-loop-through-or-enumerate-javascript-object) |
-| 128 | [How do you test for an empty object](#how-do-you-test-for-an-empty-object) |
-| 129 | [What is an arguments object](#what-is-an-arguments-object) |
-| 130 | [How do you make first letter of the string in an uppercase](#how-do-you-make-first-letter-of-the-string-in-an-uppercase) |
-| 131 | [What are the pros and cons of for loops](#what-are-the-pros-and-cons-of-for-loops) |
-| 132 | [How do you display the current date in javascript](#how-do-you-display-the-current-date-in-javascript) |
-| 133 | [How do you compare two date objects](#how-do-you-compare-two-date-objects) |
-| 134 | [How do you check if a string starts with another string](#how-do-you-check-if-a-string-starts-with-another-string) |
-| 135 | [How do you trim a string in javascript](#how-do-you-trim-a-string-in-javascript) |
-| 136 | [How do you add a key value pair in javascript](#how-do-you-add-a-key-value-pair-in-javascript) |
-| 137 | [Is the !-- notation represents a special operator](#is-the----notation-represents-a-special-operator) |
-| 138 | [How do you assign default values to variables](#how-do-you-assign-default-values-to-variables) |
-| 139 | [How do you define multiline strings](#how-do-you-define-multiline-strings) |
-| 140 | [What is an app shell model](#what-is-an-app-shell-model) |
-| 141 | [Can we define properties for functions](#can-we-define-properties-for-functions) |
-| 142 | [What is the way to find the number of parameters expected by a function](#what-is-the-way-to-find-the-number-of-parameters-expected-by-a-function) |
-| 143 | [What is a polyfill](#what-is-a-polyfill) |
-| 144 | [What are break and continue statements](#what-are-break-and-continue-statements) |
-| 145 | [What are js labels](#what-are-js-labels) |
-| 146 | [What are the benefits of keeping declarations at the top](#what-are-the-benefits-of-keeping-declarations-at-the-top) |
-| 147 | [What are the benefits of initializing variables](#what-are-the-benefits-of-initializing-variables) |
-| 148 | [What are the recommendations to create new object](#what-are-the-recommendations-to-create-new-object) |
-| 149 | [How do you define JSON arrays](#how-do-you-define-json-arrays) |
-| 150 | [How do you generate random integers](#how-do-you-generate-random-integers) |
-| 151 | [Can you write a random integers function to print integers within a range](#can-you-write-a-random-integers-function-to-print-integers-within-a-range) |
-| 152 | [What is tree shaking](#what-is-tree-shaking) |
-| 153 | [What is the need of tree shaking](#what-is-the-need-of-tree-shaking) |
-| 154 | [Is it recommended to use eval](#is-it-recommended-to-use-eval) |
-| 155 | [What is a Regular Expression](#what-is-a-regular-expression) |
-| 156 | [What are the string methods that accept Regular expression](#what-are-the-string-methods-that-accept-regular-expression) |
-| 157 | [What are modifiers in regular expression](#what-are-modifiers-in-regular-expression) |
-| 158 | [What are regular expression patterns](#what-are-regular-expression-patterns) |
-| 159 | [What is a RegExp object](#what-is-a-regexp-object) |
-| 160 | [How do you search a string for a pattern](#how-do-you-search-a-string-for-a-pattern) |
-| 161 | [What is the purpose of exec method](#what-is-the-purpose-of-exec-method) |
-| 162 | [How do you change the style of a HTML element](#how-do-you-change-the-style-of-a-html-element) |
-| 163 | [What would be the result of 1+2+'3'](#what-would-be-the-result-of-123) |
-| 164 | [What is a debugger statement](#what-is-a-debugger-statement) |
-| 165 | [What is the purpose of breakpoints in debugging](#what-is-the-purpose-of-breakpoints-in-debugging) |
-| 166 | [Can I use reserved words as identifiers](#can-i-use-reserved-words-as-identifiers) |
-| 167 | [How do you detect a mobile browser](#how-do-you-detect-a-mobile-browser) |
-| 168 | [How do you detect a mobile browser without regexp](#how-do-you-detect-a-mobile-browser-without-regexp) |
-| 169 | [How do you get the image width and height using JS](#how-do-you-get-the-image-width-and-height-using-js) |
-| 170 | [How do you make synchronous HTTP request](#how-do-you-make-synchronous-http-request) |
-| 171 | [How do you make asynchronous HTTP request](#how-do-you-make-asynchronous-http-request) |
-| 172 | [How do you convert date to another timezone in javascript](#how-do-you-convert-date-to-another-timezone-in-javascript) |
-| 173 | [What are the properties used to get size of window](#what-are-the-properties-used-to-get-size-of-window) |
-| 174 | [What is a conditional operator in javascript](#what-is-a-conditional-operator-in-javascript) |
-| 175 | [Can you apply chaining on conditional operator](#can-you-apply-chaining-on-conditional-operator) |
-| 176 | [What are the ways to execute javascript after a page load](#what-are-the-ways-to-execute-javascript-after-a-page-load) |
-| 177 | [What is the difference between proto and prototype](#what-is-the-difference-between-proto-and-prototype) |
-| 178 | [Can you give an example of when you really need a semicolon](#can-you-give-an-example-of-when-you-really-need-a-semicolon) |
-| 179 | [What is the freeze method](#what-is-the-freeze-method) |
-| 180 | [What is the purpose of the freeze method](#what-is-the-purpose-of-the-freeze-method) |
-| 181 | [Why do I need to use the freeze method](#why-do-i-need-to-use-the-freeze-method) |
-| 182 | [How do you detect a browser language preference](#how-do-you-detect-a-browser-language-preference) |
-| 183 | [How to convert a string to title case with javascript](#how-to-convert-a-string-to-title-case-with-javascript) |
-| 184 | [How do you detect if javascript is disabled on the page](#how-do-you-detect-if-javascript-is-disabled-on-the-page) |
-| 185 | [What are various operators supported by javascript](#what-are-various-operators-supported-by-javascript) |
-| 186 | [What is a rest parameter](#what-is-a-rest-parameter) |
-| 187 | [What happens if you do not use rest parameter as a last argument](#what-happens-if-you-do-not-use-rest-parameter-as-a-last-argument) |
-| 188 | [What are the bitwise operators available in javascript](#what-are-the-bitwise-operators-available-in-javascript) |
-| 189 | [What is a spread operator](#what-is-a-spread-operator) |
-| 190 | [How do you determine whether object is frozen or not](#how-do-you-determine-whether-object-is-frozen-or-not) |
-| 191 | [How do you determine two values same or not using object](#how-do-you-determine-two-values-same-or-not-using-object) |
-| 192 | [What is the purpose of using object is method](#what-is-the-purpose-of-using-object-is-method) |
-| 193 | [How do you copy properties from one object to other](#how-do-you-copy-properties-from-one-object-to-other) |
-| 194 | [What are the applications of the assign method](#what-are-the-applications-of-the-assign-method) |
-| 195 | [What is a proxy object](#what-is-a-proxy-object) |
-| 196 | [What is the purpose of the seal method](#what-is-the-purpose-of-the-seal-method) |
-| 197 | [What are the applications of the seal method](#what-are-the-applications-of-the-seal-method) |
-| 198 | [What are the differences between the freeze and seal methods](#what-are-the-differences-between-the-freeze-and-seal-methods) |
-| 199 | [How do you determine if an object is sealed or not](#how-do-you-determine-if-an-object-is-sealed-or-not) |
-| 200 | [How do you get enumerable key and value pairs](#how-do-you-get-enumerable-key-and-value-pairs) |
-| 201 | [What is the main difference between Object.values and Object.entries method](#what-is-the-main-difference-between-objectvalues-and-objectentries-method) |
-| 202 | [How can you get the list of keys of any object](#how-can-you-get-the-list-of-keys-of-any-object) |
-| 203 | [How do you create an object with a prototype](#how-do-you-create-an-object-with-a-prototype) |
-| 204 | [What is a WeakSet](#what-is-a-weakset) |
-| 205 | [What are the differences between WeakSet and Set](#what-are-the-differences-between-weakset-and-set) |
-| 206 | [List down the collection of methods available on WeakSet](#list-down-the-collection-of-methods-available-on-weakset) |
-| 207 | [What is a WeakMap](#what-is-a-weakmap) |
-| 208 | [What are the differences between WeakMap and Map](#what-are-the-differences-between-weakmap-and-map) |
-| 209 | [List down the collection of methods available on WeakMap](#list-down-the-collection-of-methods-available-on-weakmap) |
-| 210 | [What is the purpose of uneval](#what-is-the-purpose-of-uneval) |
-| 211 | [How do you encode an URL](#how-do-you-encode-an-url) |
-| 212 | [How do you decode an URL](#how-do-you-decode-an-url) |
-| 213 | [How do you print the contents of web page](#how-do-you-print-the-contents-of-web-page) |
-| 214 | [What is the difference between uneval and eval](#what-is-the-difference-between-uneval-and-eval) |
-| 215 | [What is an anonymous function](#what-is-an-anonymous-function) |
-| 216 | [What is the precedence order between local and global variables](#what-is-the-precedence-order-between-local-and-global-variables) |
-| 217 | [What are javascript accessors](#what-are-javascript-accessors) |
-| 218 | [How do you define property on Object constructor](#how-do-you-define-property-on-object-constructor) |
-| 219 | [What is the difference between get and defineProperty](#what-is-the-difference-between-get-and-defineproperty) |
-| 220 | [What are the advantages of Getters and Setters](#what-are-the-advantages-of-getters-and-setters) |
-| 221 | [Can I add getters and setters using defineProperty method](#can-i-add-getters-and-setters-using-defineproperty-method) |
-| 222 | [What is the purpose of switch-case](#what-is-the-purpose-of-switch-case) |
-| 223 | [What are the conventions to be followed for the usage of switch case](#what-are-the-conventions-to-be-followed-for-the-usage-of-switch-case) |
-| 224 | [What are primitive data types](#what-are-primitive-data-types) |
-| 225 | [What are the different ways to access object properties](#what-are-the-different-ways-to-access-object-properties) |
-| 226 | [What are the function parameter rules](#what-are-the-function-parameter-rules) |
-| 227 | [What is an error object](#what-is-an-error-object) |
-| 228 | [When do you get a syntax error](#when-do-you-get-a-syntax-error) |
-| 229 | [What are the different error names from error object](#what-are-the-different-error-names-from-error-object) |
-| 230 | [What are the various statements in error handling](#what-are-the-various-statements-in-error-handling) |
-| 231 | [What are the two types of loops in javascript](#what-are-the-two-types-of-loops-in-javascript) |
-| 232 | [What is nodejs](#what-is-nodejs) |
-| 233 | [What is the Intl object](#what-is-the-intl-object) |
-| 234 | [How do you perform language specific date and time formatting](#how-do-you-perform-language-specific-date-and-time-formatting) |
-| 235 | [What is an Iterator](#what-is-an-iterator) |
-| 236 | [How does synchronous iteration works](#how-does-synchronous-iteration-works) |
-| 237 | [What is the event loop](#what-is-the-event-loop) |
-| 238 | [What is the call stack](#what-is-the-call-stack) |
-| 239 | [What is the event queue](#what-is-the-event-queue) |
-| 240 | [What is a decorator](#what-is-a-decorator) |
-| 241 | [What are the properties of the Intl object](#what-are-the-properties-of-the-intl-object) |
-| 242 | [What is an Unary operator](#what-is-an-unary-operator) |
-| 243 | [How do you sort elements in an array](#how-do-you-sort-elements-in-an-array) |
-| 244 | [What is the purpose of compareFunction while sorting arrays](#what-is-the-purpose-of-comparefunction-while-sorting-arrays) |
-| 245 | [How do you reverse an array](#how-do-you-reverse-an-array) |
-| 246 | [How do you find the min and max values in an array](#how-do-you-find-the-min-and-max-values-in-an-array) |
-| 247 | [How do you find the min and max values without Math functions](#how-do-you-find-the-min-and-max-values-without-math-functions) |
-| 248 | [What is an empty statement and purpose of it](#what-is-an-empty-statement-and-purpose-of-it) |
-| 249 | [How do you get the metadata of a module](#how-do-you-get-the-metadata-of-a-module) |
-| 250 | [What is the comma operator](#what-is-the-comma-operator) |
-| 251 | [What is the advantage of the comma operator](#what-is-the-advantage-of-the-comma-operator) |
-| 252 | [What is typescript](#what-is-typescript) |
-| 253 | [What are the differences between javascript and typescript](#what-are-the-differences-between-javascript-and-typescript) |
-| 254 | [What are the advantages of typescript over javascript](#what-are-the-advantages-of-typescript-over-javascript) |
-| 255 | [What is an object initializer](#what-is-an-object-initializer) |
-| 256 | [What is a constructor method](#what-is-a-constructor-method) |
-| 257 | [What happens if you write constructor more than once in a class](#what-happens-if-you-write-constructor-more-than-once-in-a-class) |
-| 258 | [How do you call the constructor of a parent class](#how-do-you-call-the-constructor-of-a-parent-class) |
-| 259 | [How do you get the prototype of an object](#how-do-you-get-the-prototype-of-an-object) |
-| 260 | [What happens If I pass string type for getPrototype method](#what-happens-if-i-pass-string-type-for-getprototype-method) |
-| 261 | [How do you set the prototype of one object to another](#how-do-you-set-the-prototype-of-one-object-to-another) |
-| 262 | [How do you check whether an object can be extended or not](#how-do-you-check-whether-an-object-can-be-extended-or-not) |
-| 263 | [How do you prevent an object from being extend](#how-do-you-prevent-an-object-from-being-extend) |
-| 264 | [What are the different ways to make an object non-extensible](#what-are-the-different-ways-to-make-an-object-non-extensible) |
-| 265 | [How do you define multiple properties on an object](#how-do-you-define-multiple-properties-on-an-object) |
-| 266 | [What is the MEAN stack](#what-is-the-mean-stack) |
-| 267 | [What is obfuscation in javascript](#what-is-obfuscation-in-javascript) |
-| 268 | [Why do you need Obfuscation](#why-do-you-need-obfuscation) |
-| 269 | [What is Minification](#what-is-minification) |
-| 270 | [What are the advantages of minification](#what-are-the-advantages-of-minification) |
-| 271 | [What are the differences between obfuscation and Encryption](#what-are-the-differences-between-obfuscation-and-encryption) |
-| 272 | [What are the common tools used for minification](#what-are-the-common-tools-used-for-minification) |
-| 273 | [How do you perform form validation using javascript](#how-do-you-perform-form-validation-using-javascript) |
-| 274 | [How do you perform form validation without javascript](#how-do-you-perform-form-validation-without-javascript) |
-| 275 | [What are the DOM methods available for constraint validation](#what-are-the-dom-methods-available-for-constraint-validation) |
-| 276 | [What are the available constraint validation DOM properties](#what-are-the-available-constraint-validation-dom-properties) |
-| 277 | [What are the validity properties](#what-are-the-validity-properties) |
-| 278 | [Give an example usage of the rangeOverflow property](#give-an-example-usage-of-the-rangeoverflow-property) |
-| 279 | [Are enums available in javascript](#are-enums-available-in-javascript) |
-| 280 | [What is an enum](#what-is-an-enum) |
-| 281 | [How do you list all properties of an object](#how-do-you-list-all-properties-of-an-object) |
-| 282 | [How do you get property descriptors of an object](#how-do-you-get-property-descriptors-of-an-object) |
-| 283 | [What are the attributes provided by a property descriptor](#what-are-the-attributes-provided-by-a-property-descriptor) |
-| 284 | [How do you extend classes](#how-do-you-extend-classes) |
-| 285 | [How do I modify the url without reloading the page](#how-do-i-modify-the-url-without-reloading-the-page) |
-| 286 | [How do you check whether or not an array includes a particular value](#how-do-you-check-whether-or-not-an-array-includes-a-particular-value) |
-| 287 | [How do you compare scalar arrays](#how-do-you-compare-scalar-arrays) |
-| 288 | [How to get the value from get parameters](#how-to-get-the-value-from-get-parameters) |
-| 289 | [How do you print numbers with commas as thousand separators](#how-do-you-print-numbers-with-commas-as-thousand-separators) |
-| 290 | [What is the difference between java and javascript](#what-is-the-difference-between-java-and-javascript) |
-| 291 | [Does JavaScript support namespaces](#does-javascript-support-namespaces) |
-| 292 | [How do you declare a namespace](#how-do-you-declare-a-namespace) |
-| 293 | [How do you invoke javascript code in an iframe from the parent page](#how-do-you-invoke-javascript-code-in-an-iframe-from-the-parent-page) |
-| 294 | [How do you get the timezone offset of a date object](#how-do-you-get-the-timezone-offset-of-a-date-object) |
-| 295 | [How do you load CSS and JS files dynamically](#how-do-you-load-css-and-js-files-dynamically) |
-| 296 | [What are the different methods to find HTML elements in DOM](#what-are-the-different-methods-to-find-html-elements-in-dom) |
-| 297 | [What is jQuery](#what-is-jquery) |
-| 298 | [What is V8 JavaScript engine](#what-is-v8-javascript-engine) |
-| 299 | [Why do we call javascript as dynamic language](#why-do-we-call-javascript-as-dynamic-language) |
-| 300 | [What is a void operator](#what-is-a-void-operator) |
-| 301 | [How to set the cursor to wait](#how-to-set-the-cursor-to-wait) |
-| 302 | [How do you create an infinite loop](#how-do-you-create-an-infinite-loop) |
-| 303 | [Why do you need to avoid with statement](#why-do-you-need-to-avoid-with-statement) |
-| 304 | [What is the output of the following for loops](#what-is-the-output-of-the-following-for-loops) |
-| 305 | [List down some of the features of ES6](#list-down-some-of-the-features-of-es6) |
-| 306 | [What is ES6](#what-is-es6) |
-| 307 | [Can I redeclare let and const variables](#can-i-redeclare-let-and-const-variables) |
-| 308 | [Does the `const` variable make the value immutable](#does-the-const-variable-make-the-value-immutable) |
-| 309 | [What are default parameters](#what-are-default-parameters) |
-| 310 | [What are template literals](#what-are-template-literals) |
-| 311 | [How do you write multi-line strings in template literals](#how-do-you-write-multi-line-strings-in-template-literals) |
-| 312 | [What are nesting templates](#what-are-nesting-templates) |
-| 313 | [What are tagged templates](#what-are-tagged-templates) |
-| 314 | [What are raw strings](#what-are-raw-strings) |
-| 315 | [What is destructuring assignment](#what-is-destructuring-assignment) |
-| 316 | [What are default values in destructuring assignment](#what-are-default-values-in-destructuring-assignment) |
-| 317 | [How do you swap variables in destructuring assignment](#how-do-you-swap-variables-in-destructuring-assignment) |
-| 318 | [What are enhanced object literals](#what-are-enhanced-object-literals) |
-| 319 | [What are dynamic imports](#what-are-dynamic-imports) |
-| 320 | [What are the use cases for dynamic imports](#what-are-the-use-cases-for-dynamic-imports) |
-| 321 | [What are typed arrays](#what-are-typed-arrays) |
-| 322 | [What are the advantages of module loaders](#what-are-the-advantages-of-module-loaders) |
-| 323 | [What is collation](#what-is-collation) |
-| 324 | [What is for...of statement](#what-is-forof-statement) |
-| 325 | [What is the output of below spread operator array](#what-is-the-output-of-below-spread-operator-array) |
-| 326 | [Is PostMessage secure](#is-postmessage-secure) |
-| 327 | [What are the problems with postmessage target origin as wildcard](#what-are-the-problems-with-postmessage-target-origin-as-wildcard) |
-| 328 | [How do you avoid receiving postMessages from attackers](#how-do-you-avoid-receiving-postmessages-from-attackers) |
-| 329 | [Can I avoid using postMessages completely](#can-i-avoid-using-postmessages-completely) |
-| 330 | [Is postMessages synchronous](#is-postmessages-synchronous) |
-| 331 | [What paradigm is Javascript](#what-paradigm-is-javascript) |
-| 332 | [What is the difference between internal and external javascript](#what-is-the-difference-between-internal-and-external-javascript) |
-| 333 | [Is JavaScript faster than server side script](#is-javascript-faster-than-server-side-script) |
-| 334 | [How do you get the status of a checkbox](#how-do-you-get-the-status-of-a-checkbox) |
-| 335 | [What is the purpose of double tilde operator](#what-is-the-purpose-of-double-tilde-operator) |
-| 336 | [How do you convert character to ASCII code](#how-do-you-convert-character-to-ascii-code) |
-| 337 | [What is ArrayBuffer](#what-is-arraybuffer) |
-| 338 | [What is the output of below string expression](#what-is-the-output-of-below-string-expression) |
-| 339 | [What is the purpose of Error object](#what-is-the-purpose-of-error-object) |
-| 340 | [What is the purpose of EvalError object](#what-is-the-purpose-of-evalerror-object) |
-| 341 | [What are the list of cases error thrown from non-strict mode to strict mode](#what-are-the-list-of-cases-error-thrown-from-non-strict-mode-to-strict-mode) |
-| 342 | [Do all objects have prototypes](#do-all-objects-have-prototypes) |
-| 343 | [What is the difference between a parameter and an argument](#what-is-the-difference-between-a-parameter-and-an-argument) |
-| 344 | [What is the purpose of some method in arrays](#what-is-the-purpose-of-some-method-in-arrays) |
-| 345 | [How do you combine two or more arrays](#how-do-you-combine-two-or-more-arrays) |
-| 346 | [What is the difference between Shallow and Deep copy](#what-is-the-difference-between-shallow-and-deep-copy) |
-| 347 | [How do you create specific number of copies of a string](#how-do-you-create-specific-number-of-copies-of-a-string) |
-| 348 | [How do you return all matching strings against a regular expression](#how-do-you-return-all-matching-strings-against-a-regular-expression) |
-| 349 | [How do you trim a string at the beginning or ending](#how-do-you-trim-a-string-at-the-beginning-or-ending) |
-| 350 | [What is the output of below console statement with unary operator](#what-is-the-output-of-below-console-statement-with-unary-operator) |
-| 351 | [Does javascript uses mixins](#does-javascript-uses-mixins) |
-| 352 | [Mixin Example using Object composition](#mixin-example-using-object-composition) |
-| 353 | [Benefits](#benefits) |
-| 354 | [What is a thunk function](#what-is-a-thunk-function) |
-| 355 | [What are asynchronous thunks](#what-are-asynchronous-thunks) |
-| 356 | [What is the output of below function calls](#what-is-the-output-of-below-function-calls) |
-| 357 | [How to remove all line breaks from a string](#how-to-remove-all-line-breaks-from-a-string) |
-| 358 | [What is the difference between reflow and repaint](#what-is-the-difference-between-reflow-and-repaint) |
-| 359 | [What happens with negating an array](#what-happens-with-negating-an-array) |
-| 360 | [What happens if we add two arrays](#what-happens-if-we-add-two-arrays) |
-| 361 | [What is the output of prepend additive operator on falsy values](#what-is-the-output-of-prepend-additive-operator-on-falsy-values) |
-| 362 | [How do you create self string using special characters](#how-do-you-create-self-string-using-special-characters) |
-| 363 | [How do you remove falsy values from an array](#how-do-you-remove-falsy-values-from-an-array) |
-| 364 | [How do you get unique values of an array](#how-do-you-get-unique-values-of-an-array) |
-| 365 | [What is destructuring aliases](#what-is-destructuring-aliases) |
-| 366 | [How do you map the array values without using map method](#how-do-you-map-the-array-values-without-using-map-method) |
-| 367 | [How do you empty an array](#how-do-you-empty-an-array) |
-| 368 | [How do you round numbers to certain decimals](#how-do-you-round-numbers-to-certain-decimals) |
-| 369 | [What is the easiest way to convert an array to an object](#what-is-the-easiest-way-to-convert-an-array-to-an-object) |
-| 370 | [How do you create an array with some data](#how-do-you-create-an-array-with-some-data) |
-| 371 | [What are the placeholders from console object](#what-are-the-placeholders-from-console-object) |
-| 372 | [Is it possible to add CSS to console messages](#is-it-possible-to-add-css-to-console-messages) |
-| 373 | [What is the purpose of dir method of console object](#what-is-the-purpose-of-dir-method-of-console-object) |
-| 374 | [Is it possible to debug HTML elements in console](#is-it-possible-to-debug-html-elements-in-console) |
-| 375 | [How do you display data in a tabular format using console object](#how-do-you-display-data-in-a-tabular-format-using-console-object) |
-| 376 | [How do you verify that an argument is a Number or not](#how-do-you-verify-that-an-argument-is-a-number-or-not) |
-| 377 | [How do you create copy to clipboard button](#how-do-you-create-copy-to-clipboard-button) |
-| 378 | [What is the shortcut to get timestamp](#what-is-the-shortcut-to-get-timestamp) |
-| 379 | [How do you flattening multi dimensional arrays](#how-do-you-flattening-multi-dimensional-arrays) |
-| 380 | [What is the easiest multi condition checking](#what-is-the-easiest-multi-condition-checking) |
-| 381 | [How do you capture browser back button](#how-do-you-capture-browser-back-button) |
-| 382 | [How do you disable right click in the web page](#how-do-you-disable-right-click-in-the-web-page) |
-| 383 | [What are wrapper objects](#what-are-wrapper-objects) |
-| 384 | [What is AJAX](#what-is-ajax) |
-| 385 | [What are the different ways to deal with Asynchronous Code](#what-are-the-different-ways-to-deal-with-asynchronous-code) |
-| 386 | [How to cancel a fetch request](#how-to-cancel-a-fetch-request) |
-| 387 | [What is web speech API](#what-is-web-speech-api) |
-| 388 | [What is minimum timeout throttling](#what-is-minimum-timeout-throttling) |
-| 389 | [How do you implement zero timeout in modern browsers](#how-do-you-implement-zero-timeout-in-modern-browsers) |
-| 390 | [What are tasks in event loop](#what-are-tasks-in-event-loop) |
-| 391 | [What is microtask](#what-is-microtask) |
-| 392 | [What are different event loops](#what-are-different-event-loops) |
-| 393 | [What is the purpose of queueMicrotask](#what-is-the-purpose-of-queuemicrotask) |
-| 394 | [How do you use javascript libraries in typescript file](#how-do-you-use-javascript-libraries-in-typescript-file) |
-| 395 | [What are the differences between promises and observables](#what-are-the-differences-between-promises-and-observables) |
-| 396 | [What is heap](#what-is-heap) |
-| 397 | [What is an event table](#what-is-an-event-table) |
-| 398 | [What is a microTask queue](#what-is-a-microtask-queue) |
-| 399 | [What is the difference between shim and polyfill](#what-is-the-difference-between-shim-and-polyfill) |
-| 400 | [How do you detect primitive or non primitive value type](#how-do-you-detect-primitive-or-non-primitive-value-type) |
-| 401 | [What is babel](#what-is-babel) |
-| 402 | [Is Node.js completely single threaded](#is-nodejs-completely-single-threaded) |
-| 403 | [What are the common use cases of observables](#what-are-the-common-use-cases-of-observables) |
-| 404 | [What is RxJS](#what-is-rxjs) |
+
+| No. | Questions |
+| --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| 1 | [What are the possible ways to create objects in JavaScript](#what-are-the-possible-ways-to-create-objects-in-javascript) |
+| 2 | [What is a prototype chain](#what-is-a-prototype-chain) |
+| 3 | [What is the Difference Between `call`, `apply`, and `bind`](#what-is-the-difference-between-call-apply-and-bind) |
+| 4 | [What is JSON and its common operations](#what-is-json-and-its-common-operations) |
+| 5 | [What is the purpose of the array slice method](#what-is-the-purpose-of-the-array-slice-method) |
+| 6 | [What is the purpose of the array splice method](#what-is-the-purpose-of-the-array-splice-method) |
+| 7 | [What is the difference between slice and splice](#what-is-the-difference-between-slice-and-splice) |
+| 8 | [How do you compare Object and Map](#how-do-you-compare-object-and-map) |
+| 9 | [What is the difference between == and === operators](#what-is-the-difference-between--and--operators) |
+| 10 | [What are lambda expressions or arrow functions](#what-are-lambda-expressions-or-arrow-functions) |
+| 11 | [What is a first class function](#what-is-a-first-class-function) |
+| 12 | [What is a first order function](#what-is-a-first-order-function) |
+| 13 | [What is a higher order function](#what-is-a-higher-order-function) |
+| 14 | [What is a unary function](#what-is-a-unary-function) |
+| 15 | [What is the currying function](#what-is-the-currying-function) |
+| 16 | [What is a pure function](#what-is-a-pure-function) |
+| 17 | [What are the benefits of pure functions](#what-are-the-benefits-of-pure-functions) |
+| 18 | [What is the purpose of the let keyword](#what-is-the-purpose-of-the-let-keyword) |
+| 19 | [What is the difference between let and var](#what-is-the-difference-between-let-and-var) |
+| 20 | [What is the reason to choose the name let as a keyword](#what-is-the-reason-to-choose-the-name-let-as-a-keyword) |
+| 21 | [How do you redeclare variables in a switch block without an error](#how-do-you-redeclare-variables-in-a-switch-block-without-an-error) |
+| 22 | [What is the Temporal Dead Zone](#what-is-the-temporal-dead-zone) |
+| 23 | [What is an IIFE (Immediately Invoked Function Expression)](#what-is-an-iife-immediately-invoked-function-expression) |
+| 24 | [How do you decode or encode a URL in JavaScript?](#how-do-you-decode-or-encode-a-url-in-javascript) |
+| 25 | [What is memoization](#what-is-memoization) |
+| 26 | [What is Hoisting](#what-is-hoisting) |
+| 27 | [What are classes in ES6](#what-are-classes-in-es6) |
+| 28 | [What are closures](#what-are-closures) |
+| 29 | [What are modules](#what-are-modules) |
+| 30 | [Why do you need modules](#why-do-you-need-modules) |
+| 31 | [What is scope in javascript](#what-is-scope-in-javascript) |
+| 32 | [What is a service worker](#what-is-a-service-worker) |
+| 33 | [How do you manipulate DOM using a service worker](#how-do-you-manipulate-dom-using-a-service-worker) |
+| 34 | [How do you reuse information across service worker restarts](#how-do-you-reuse-information-across-service-worker-restarts) |
+| 35 | [What is IndexedDB](#what-is-indexeddb) |
+| 36 | [What is web storage](#what-is-web-storage) |
+| 37 | [What is a post message](#what-is-a-post-message) |
+| 38 | [What is a Cookie](#what-is-a-cookie) |
+| 39 | [Why do you need a Cookie](#why-do-you-need-a-cookie) |
+| 40 | [What are the options in a cookie](#what-are-the-options-in-a-cookie) |
+| 41 | [How do you delete a cookie](#how-do-you-delete-a-cookie) |
+| 42 | [What are the differences between cookie, local storage and session storage](#what-are-the-differences-between-cookie-local-storage-and-session-storage) |
+| 43 | [What is the main difference between localStorage and sessionStorage](#what-is-the-main-difference-between-localstorage-and-sessionstorage) |
+| 44 | [How do you access web storage](#how-do-you-access-web-storage) |
+| 45 | [What are the methods available on session storage](#what-are-the-methods-available-on-session-storage) |
+| 46 | [What is a storage event and its event handler](#what-is-a-storage-event-and-its-event-handler) |
+| 47 | [Why do you need web storage](#why-do-you-need-web-storage) |
+| 48 | [How do you check web storage browser support](#how-do-you-check-web-storage-browser-support) |
+| 49 | [How do you check web workers browser support](#how-do-you-check-web-workers-browser-support) |
+| 50 | [Give an example of a web worker](#give-an-example-of-a-web-worker) |
+| 51 | [What are the restrictions of web workers on DOM](#what-are-the-restrictions-of-web-workers-on-dom) |
+| 52 | [What is a promise](#what-is-a-promise) |
+| 53 | [Why do you need a promise](#why-do-you-need-a-promise) |
+| 54 | [Explain the three states of promise](#explain-the-three-states-of-promise) |
+| 55 | [What is a callback function](#what-is-a-callback-function) |
+| 56 | [Why do we need callbacks](#why-do-we-need-callbacks) |
+| 57 | [What is a callback hell](#what-is-a-callback-hell) |
+| 58 | [What are server-sent events](#what-are-server-sent-events) |
+| 59 | [How do you receive server-sent event notifications](#how-do-you-receive-server-sent-event-notifications) |
+| 60 | [How do you check browser support for server-sent events](#how-do-you-check-browser-support-for-server-sent-events) |
+| 61 | [What are the events available for server sent events](#what-are-the-events-available-for-server-sent-events) |
+| 62 | [What are the main rules of promise](#what-are-the-main-rules-of-promise) |
+| 63 | [What is callback in callback](#what-is-callback-in-callback) |
+| 64 | [What is promise chaining](#what-is-promise-chaining) |
+| 65 | [What is promise.all](#what-is-promiseall) |
+| 66 | [What is the purpose of the race method in promise](#what-is-the-purpose-of-the-race-method-in-promise) |
+| 67 | [What is a strict mode in javascript](#what-is-a-strict-mode-in-javascript) |
+| 68 | [Why do you need strict mode](#why-do-you-need-strict-mode) |
+| 69 | [How do you declare strict mode](#how-do-you-declare-strict-mode) |
+| 70 | [What is the purpose of double exclamation](#what-is-the-purpose-of-double-exclamation) |
+| 71 | [What is the purpose of the delete operator](#what-is-the-purpose-of-the-delete-operator) |
+| 72 | [What is typeof operator](#what-is-typeof-operator) |
+| 73 | [What is undefined property](#what-is-undefined-property) |
+| 74 | [What is null value](#what-is-null-value) |
+| 75 | [What is the difference between null and undefined](#what-is-the-difference-between-null-and-undefined) |
+| 76 | [What is eval](#what-is-eval) |
+| 77 | [What is the difference between window and document](#what-is-the-difference-between-window-and-document) |
+| 78 | [How do you access history in javascript](#how-do-you-access-history-in-javascript) |
+| 79 | [How do you detect caps lock key turned on or not](#how-do-you-detect-caps-lock-key-turned-on-or-not) |
+| 80 | [What is isNaN](#what-is-isnan) |
+| 81 | [What are the differences between undeclared and undefined variables](#what-are-the-differences-between-undeclared-and-undefined-variables) |
+| 82 | [What are global variables](#what-are-global-variables) |
+| 83 | [What are the problems with global variables](#what-are-the-problems-with-global-variables) |
+| 84 | [What is NaN property](#what-is-nan-property) |
+| 85 | [What is the purpose of isFinite function](#what-is-the-purpose-of-isfinite-function) |
+| 86 | [What is an event flow](#what-is-an-event-flow) |
+| 87 | [What is event capturing](#what-is-event-capturing) |
+| 88 | [What is event bubbling](#what-is-event-bubbling) |
+| 89 | [How do you submit a form using JavaScript](#how-do-you-submit-a-form-using-javascript) |
+| 90 | [How do you find operating system details](#how-do-you-find-operating-system-details) |
+| 91 | [What is the difference between document load and DOMContentLoaded events](#what-is-the-difference-between-document-load-and-domcontentloaded-events) |
+| 92 | [What is the difference between native, host and user objects](#what-is-the-difference-between-native-host-and-user-objects) |
+| 93 | [What are the tools or techniques used for debugging JavaScript code](#what-are-the-tools-or-techniques-used-for-debugging-javascript-code) |
+| 94 | [What are the pros and cons of promises over callbacks](#what-are-the-pros-and-cons-of-promises-over-callbacks) |
+| 95 | [What is the difference between an attribute and a property](#what-is-the-difference-between-an-attribute-and-a-property) |
+| 96 | [What is same-origin policy](#what-is-same-origin-policy) |
+| 97 | [What is the purpose of void 0](#what-is-the-purpose-of-void-0) |
+| 98 | [Is JavaScript a compiled or interpreted language](#is-javascript-a-compiled-or-interpreted-language) |
+| 99 | [Is JavaScript a case-sensitive language](#is-javascript-a-case-sensitive-language) |
+| 100 | [Is there any relation between Java and JavaScript](#is-there-any-relation-between-java-and-javascript) |
+| 101 | [What are events](#what-are-events) |
+| 102 | [Who created javascript](#who-created-javascript) |
+| 103 | [What is the use of preventDefault method](#what-is-the-use-of-preventdefault-method) |
+| 104 | [What is the use of stopPropagation method](#what-is-the-use-of-stoppropagation-method) |
+| 105 | [What are the steps involved in return false usage](#what-are-the-steps-involved-in-return-false-usage) |
+| 106 | [What is BOM](#what-is-bom) |
+| 107 | [What is the use of setTimeout](#what-is-the-use-of-settimeout) |
+| 108 | [What is the use of setInterval](#what-is-the-use-of-setinterval) |
+| 109 | [Why is JavaScript treated as Single threaded](#why-is-javascript-treated-as-single-threaded) |
+| 110 | [What is an event delegation](#what-is-an-event-delegation) |
+| 111 | [What is ECMAScript](#what-is-ecmascript) |
+| 112 | [What is JSON](#what-is-json) |
+| 113 | [What are the syntax rules of JSON](#what-are-the-syntax-rules-of-json) |
+| 114 | [What is the purpose JSON stringify](#what-is-the-purpose-json-stringify) |
+| 115 | [How do you parse JSON string](#how-do-you-parse-json-string) |
+| 116 | [Why do you need JSON](#why-do-you-need-json) |
+| 117 | [What are PWAs](#what-are-pwas) |
+| 118 | [What is the purpose of clearTimeout method](#what-is-the-purpose-of-cleartimeout-method) |
+| 119 | [What is the purpose of clearInterval method](#what-is-the-purpose-of-clearinterval-method) |
+| 120 | [How do you redirect new page in javascript](#how-do-you-redirect-new-page-in-javascript) |
+| 121 | [How do you check whether a string contains a substring](#how-do-you-check-whether-a-string-contains-a-substring) |
+| 122 | [How do you validate an email in javascript](#how-do-you-validate-an-email-in-javascript) |
+| 123 | [How do you get the current url with javascript](#how-do-you-get-the-current-url-with-javascript) |
+| 124 | [What are the various url properties of location object](#what-are-the-various-url-properties-of-location-object) |
+| 125 | [How do get query string values in javascript](#how-do-get-query-string-values-in-javascript) |
+| 126 | [How do you check if a key exists in an object](#how-do-you-check-if-a-key-exists-in-an-object) |
+| 127 | [How do you loop through or enumerate javascript object](#how-do-you-loop-through-or-enumerate-javascript-object) |
+| 128 | [How do you test for an empty object](#how-do-you-test-for-an-empty-object) |
+| 129 | [What is an arguments object](#what-is-an-arguments-object) |
+| 130 | [How do you make first letter of the string in an uppercase](#how-do-you-make-first-letter-of-the-string-in-an-uppercase) |
+| 131 | [What are the pros and cons of for loops](#what-are-the-pros-and-cons-of-for-loops) |
+| 132 | [How do you display the current date in javascript](#how-do-you-display-the-current-date-in-javascript) |
+| 133 | [How do you compare two date objects](#how-do-you-compare-two-date-objects) |
+| 134 | [How do you check if a string starts with another string](#how-do-you-check-if-a-string-starts-with-another-string) |
+| 135 | [How do you trim a string in javascript](#how-do-you-trim-a-string-in-javascript) |
+| 136 | [How do you add a key value pair in javascript](#how-do-you-add-a-key-value-pair-in-javascript) |
+| 137 | [Is the !-- notation represents a special operator](#is-the----notation-represents-a-special-operator) |
+| 138 | [How do you assign default values to variables](#how-do-you-assign-default-values-to-variables) |
+| 139 | [How do you define multiline strings](#how-do-you-define-multiline-strings) |
+| 140 | [What is an app shell model](#what-is-an-app-shell-model) |
+| 141 | [Can we define properties for functions](#can-we-define-properties-for-functions) |
+| 142 | [What is the way to find the number of parameters expected by a function](#what-is-the-way-to-find-the-number-of-parameters-expected-by-a-function) |
+| 143 | [What is a polyfill](#what-is-a-polyfill) |
+| 144 | [What are break and continue statements](#what-are-break-and-continue-statements) |
+| 145 | [What are js labels](#what-are-js-labels) |
+| 146 | [What are the benefits of keeping declarations at the top](#what-are-the-benefits-of-keeping-declarations-at-the-top) |
+| 147 | [What are the benefits of initializing variables](#what-are-the-benefits-of-initializing-variables) |
+| 148 | [What are the recommendations to create new object](#what-are-the-recommendations-to-create-new-object) |
+| 149 | [How do you define JSON arrays](#how-do-you-define-json-arrays) |
+| 150 | [How do you generate random integers](#how-do-you-generate-random-integers) |
+| 151 | [Can you write a random integers function to print integers within a range](#can-you-write-a-random-integers-function-to-print-integers-within-a-range) |
+| 152 | [What is tree shaking](#what-is-tree-shaking) |
+| 153 | [What is the need of tree shaking](#what-is-the-need-of-tree-shaking) |
+| 154 | [Is it recommended to use eval](#is-it-recommended-to-use-eval) |
+| 155 | [What is a Regular Expression](#what-is-a-regular-expression) |
+| 156 | [What are the string methods that accept Regular expression](#what-are-the-string-methods-that-accept-regular-expression) |
+| 157 | [What are modifiers in regular expression](#what-are-modifiers-in-regular-expression) |
+| 158 | [What are regular expression patterns](#what-are-regular-expression-patterns) |
+| 159 | [What is a RegExp object](#what-is-a-regexp-object) |
+| 160 | [How do you search a string for a pattern](#how-do-you-search-a-string-for-a-pattern) |
+| 161 | [What is the purpose of exec method](#what-is-the-purpose-of-exec-method) |
+| 162 | [How do you change the style of a HTML element](#how-do-you-change-the-style-of-a-html-element) |
+| 163 | [What would be the result of 1+2+'3'](#what-would-be-the-result-of-123) |
+| 164 | [What is a debugger statement](#what-is-a-debugger-statement) |
+| 165 | [What is the purpose of breakpoints in debugging](#what-is-the-purpose-of-breakpoints-in-debugging) |
+| 166 | [Can I use reserved words as identifiers](#can-i-use-reserved-words-as-identifiers) |
+| 167 | [How do you detect a mobile browser](#how-do-you-detect-a-mobile-browser) |
+| 168 | [How do you detect a mobile browser without regexp](#how-do-you-detect-a-mobile-browser-without-regexp) |
+| 169 | [How do you get the image width and height using JS](#how-do-you-get-the-image-width-and-height-using-js) |
+| 170 | [How do you make synchronous HTTP request](#how-do-you-make-synchronous-http-request) |
+| 171 | [How do you make asynchronous HTTP request](#how-do-you-make-asynchronous-http-request) |
+| 172 | [How do you convert date to another timezone in javascript](#how-do-you-convert-date-to-another-timezone-in-javascript) |
+| 173 | [What are the properties used to get size of window](#what-are-the-properties-used-to-get-size-of-window) |
+| 174 | [What is a conditional operator in javascript](#what-is-a-conditional-operator-in-javascript) |
+| 175 | [Can you apply chaining on conditional operator](#can-you-apply-chaining-on-conditional-operator) |
+| 176 | [What are the ways to execute javascript after a page load](#what-are-the-ways-to-execute-javascript-after-a-page-load) |
+| 177 | [What is the difference between proto and prototype](#what-is-the-difference-between-proto-and-prototype) |
+| 178 | [Can you give an example of when you really need a semicolon](#can-you-give-an-example-of-when-you-really-need-a-semicolon) |
+| 179 | [What is the freeze method](#what-is-the-freeze-method) |
+| 180 | [What is the purpose of the freeze method](#what-is-the-purpose-of-the-freeze-method) |
+| 181 | [Why do I need to use the freeze method](#why-do-i-need-to-use-the-freeze-method) |
+| 182 | [How do you detect a browser language preference](#how-do-you-detect-a-browser-language-preference) |
+| 183 | [How to convert a string to title case with javascript](#how-to-convert-a-string-to-title-case-with-javascript) |
+| 184 | [How do you detect if javascript is disabled on the page](#how-do-you-detect-if-javascript-is-disabled-on-the-page) |
+| 185 | [What are various operators supported by javascript](#what-are-various-operators-supported-by-javascript) |
+| 186 | [What is a rest parameter](#what-is-a-rest-parameter) |
+| 187 | [What happens if you do not use rest parameter as a last argument](#what-happens-if-you-do-not-use-rest-parameter-as-a-last-argument) |
+| 188 | [What are the bitwise operators available in javascript](#what-are-the-bitwise-operators-available-in-javascript) |
+| 189 | [What is a spread operator](#what-is-a-spread-operator) |
+| 190 | [How do you determine whether object is frozen or not](#how-do-you-determine-whether-object-is-frozen-or-not) |
+| 191 | [How do you determine two values same or not using object](#how-do-you-determine-two-values-same-or-not-using-object) |
+| 192 | [What is the purpose of using object is method](#what-is-the-purpose-of-using-object-is-method) |
+| 193 | [How do you copy properties from one object to other](#how-do-you-copy-properties-from-one-object-to-other) |
+| 194 | [What are the applications of the assign method](#what-are-the-applications-of-the-assign-method) |
+| 195 | [What is a proxy object](#what-is-a-proxy-object) |
+| 196 | [What is the purpose of the seal method](#what-is-the-purpose-of-the-seal-method) |
+| 197 | [What are the applications of the seal method](#what-are-the-applications-of-the-seal-method) |
+| 198 | [What are the differences between the freeze and seal methods](#what-are-the-differences-between-the-freeze-and-seal-methods) |
+| 199 | [How do you determine if an object is sealed or not](#how-do-you-determine-if-an-object-is-sealed-or-not) |
+| 200 | [How do you get enumerable key and value pairs](#how-do-you-get-enumerable-key-and-value-pairs) |
+| 201 | [What is the main difference between Object.values and Object.entries method](#what-is-the-main-difference-between-objectvalues-and-objectentries-method) |
+| 202 | [How can you get the list of keys of any object](#how-can-you-get-the-list-of-keys-of-any-object) |
+| 203 | [How do you create an object with a prototype](#how-do-you-create-an-object-with-a-prototype) |
+| 204 | [What is a WeakSet](#what-is-a-weakset) |
+| 205 | [What are the differences between WeakSet and Set](#what-are-the-differences-between-weakset-and-set) |
+| 206 | [List down the collection of methods available on WeakSet](#list-down-the-collection-of-methods-available-on-weakset) |
+| 207 | [What is a WeakMap](#what-is-a-weakmap) |
+| 208 | [What are the differences between WeakMap and Map](#what-are-the-differences-between-weakmap-and-map) |
+| 209 | [List down the collection of methods available on WeakMap](#list-down-the-collection-of-methods-available-on-weakmap) |
+| 210 | [What is the purpose of uneval](#what-is-the-purpose-of-uneval) |
+| 211 | [How do you encode an URL](#how-do-you-encode-an-url) |
+| 212 | [How do you decode an URL](#how-do-you-decode-an-url) |
+| 213 | [How do you print the contents of web page](#how-do-you-print-the-contents-of-web-page) |
+| 214 | [What is the difference between uneval and eval](#what-is-the-difference-between-uneval-and-eval) |
+| 215 | [What is an anonymous function](#what-is-an-anonymous-function) |
+| 216 | [What is the precedence order between local and global variables](#what-is-the-precedence-order-between-local-and-global-variables) |
+| 217 | [What are javascript accessors](#what-are-javascript-accessors) |
+| 218 | [How do you define property on Object constructor](#how-do-you-define-property-on-object-constructor) |
+| 219 | [What is the difference between get and defineProperty](#what-is-the-difference-between-get-and-defineproperty) |
+| 220 | [What are the advantages of Getters and Setters](#what-are-the-advantages-of-getters-and-setters) |
+| 221 | [Can I add getters and setters using defineProperty method](#can-i-add-getters-and-setters-using-defineproperty-method) |
+| 222 | [What is the purpose of switch-case](#what-is-the-purpose-of-switch-case) |
+| 223 | [What are the conventions to be followed for the usage of switch case](#what-are-the-conventions-to-be-followed-for-the-usage-of-switch-case) |
+| 224 | [What are primitive data types](#what-are-primitive-data-types) |
+| 225 | [What are the different ways to access object properties](#what-are-the-different-ways-to-access-object-properties) |
+| 226 | [What are the function parameter rules](#what-are-the-function-parameter-rules) |
+| 227 | [What is an error object](#what-is-an-error-object) |
+| 228 | [When do you get a syntax error](#when-do-you-get-a-syntax-error) |
+| 229 | [What are the different error names from error object](#what-are-the-different-error-names-from-error-object) |
+| 230 | [What are the various statements in error handling](#what-are-the-various-statements-in-error-handling) |
+| 231 | [What are the two types of loops in javascript](#what-are-the-two-types-of-loops-in-javascript) |
+| 232 | [What is nodejs](#what-is-nodejs) |
+| 233 | [What is the Intl object](#what-is-the-intl-object) |
+| 234 | [How do you perform language specific date and time formatting](#how-do-you-perform-language-specific-date-and-time-formatting) |
+| 235 | [What is an Iterator](#what-is-an-iterator) |
+| 236 | [How does synchronous iteration works](#how-does-synchronous-iteration-works) |
+| 237 | [What is the event loop](#what-is-the-event-loop) |
+| 238 | [What is the call stack](#what-is-the-call-stack) |
+| 239 | [What is the event queue](#what-is-the-event-queue) |
+| 240 | [What is a decorator](#what-is-a-decorator) |
+| 241 | [What are the properties of the Intl object](#what-are-the-properties-of-the-intl-object) |
+| 242 | [What is an Unary operator](#what-is-an-unary-operator) |
+| 243 | [How do you sort elements in an array](#how-do-you-sort-elements-in-an-array) |
+| 244 | [What is the purpose of compareFunction while sorting arrays](#what-is-the-purpose-of-comparefunction-while-sorting-arrays) |
+| 245 | [How do you reverse an array](#how-do-you-reverse-an-array) |
+| 246 | [How do you find the min and max values in an array](#how-do-you-find-the-min-and-max-values-in-an-array) |
+| 247 | [How do you find the min and max values without Math functions](#how-do-you-find-the-min-and-max-values-without-math-functions) |
+| 248 | [What is an empty statement and purpose of it](#what-is-an-empty-statement-and-purpose-of-it) |
+| 249 | [How do you get the metadata of a module](#how-do-you-get-the-metadata-of-a-module) |
+| 250 | [What is the comma operator](#what-is-the-comma-operator) |
+| 251 | [What is the advantage of the comma operator](#what-is-the-advantage-of-the-comma-operator) |
+| 252 | [What is typescript](#what-is-typescript) |
+| 253 | [What are the differences between javascript and typescript](#what-are-the-differences-between-javascript-and-typescript) |
+| 254 | [What are the advantages of typescript over javascript](#what-are-the-advantages-of-typescript-over-javascript) |
+| 255 | [What is an object initializer](#what-is-an-object-initializer) |
+| 256 | [What is a constructor method](#what-is-a-constructor-method) |
+| 257 | [What happens if you write constructor more than once in a class](#what-happens-if-you-write-constructor-more-than-once-in-a-class) |
+| 258 | [How do you call the constructor of a parent class](#how-do-you-call-the-constructor-of-a-parent-class) |
+| 259 | [How do you get the prototype of an object](#how-do-you-get-the-prototype-of-an-object) |
+| 260 | [What happens If I pass string type for getPrototype method](#what-happens-if-i-pass-string-type-for-getprototype-method) |
+| 261 | [How do you set the prototype of one object to another](#how-do-you-set-the-prototype-of-one-object-to-another) |
+| 262 | [How do you check whether an object can be extended or not](#how-do-you-check-whether-an-object-can-be-extended-or-not) |
+| 263 | [How do you prevent an object from being extend](#how-do-you-prevent-an-object-from-being-extend) |
+| 264 | [What are the different ways to make an object non-extensible](#what-are-the-different-ways-to-make-an-object-non-extensible) |
+| 265 | [How do you define multiple properties on an object](#how-do-you-define-multiple-properties-on-an-object) |
+| 266 | [What is the MEAN stack](#what-is-the-mean-stack) |
+| 267 | [What is obfuscation in javascript](#what-is-obfuscation-in-javascript) |
+| 268 | [Why do you need Obfuscation](#why-do-you-need-obfuscation) |
+| 269 | [What is Minification](#what-is-minification) |
+| 270 | [What are the advantages of minification](#what-are-the-advantages-of-minification) |
+| 271 | [What are the differences between obfuscation and Encryption](#what-are-the-differences-between-obfuscation-and-encryption) |
+| 272 | [What are the common tools used for minification](#what-are-the-common-tools-used-for-minification) |
+| 273 | [How do you perform form validation using javascript](#how-do-you-perform-form-validation-using-javascript) |
+| 274 | [How do you perform form validation without javascript](#how-do-you-perform-form-validation-without-javascript) |
+| 275 | [What are the DOM methods available for constraint validation](#what-are-the-dom-methods-available-for-constraint-validation) |
+| 276 | [What are the available constraint validation DOM properties](#what-are-the-available-constraint-validation-dom-properties) |
+| 277 | [What are the validity properties](#what-are-the-validity-properties) |
+| 278 | [Give an example usage of the rangeOverflow property](#give-an-example-usage-of-the-rangeoverflow-property) |
+| 279 | [Are enums available in javascript](#are-enums-available-in-javascript) |
+| 280 | [What is an enum](#what-is-an-enum) |
+| 281 | [How do you list all properties of an object](#how-do-you-list-all-properties-of-an-object) |
+| 282 | [How do you get property descriptors of an object](#how-do-you-get-property-descriptors-of-an-object) |
+| 283 | [What are the attributes provided by a property descriptor](#what-are-the-attributes-provided-by-a-property-descriptor) |
+| 284 | [How do you extend classes](#how-do-you-extend-classes) |
+| 285 | [How do I modify the url without reloading the page](#how-do-i-modify-the-url-without-reloading-the-page) |
+| 286 | [How do you check whether or not an array includes a particular value](#how-do-you-check-whether-or-not-an-array-includes-a-particular-value) |
+| 287 | [How do you compare scalar arrays](#how-do-you-compare-scalar-arrays) |
+| 288 | [How to get the value from get parameters](#how-to-get-the-value-from-get-parameters) |
+| 289 | [How do you print numbers with commas as thousand separators](#how-do-you-print-numbers-with-commas-as-thousand-separators) |
+| 290 | [What is the difference between java and javascript](#what-is-the-difference-between-java-and-javascript) |
+| 291 | [Does JavaScript support namespaces](#does-javascript-support-namespaces) |
+| 292 | [How do you declare a namespace](#how-do-you-declare-a-namespace) |
+| 293 | [How do you invoke javascript code in an iframe from the parent page](#how-do-you-invoke-javascript-code-in-an-iframe-from-the-parent-page) |
+| 294 | [How do you get the timezone offset of a date object](#how-do-you-get-the-timezone-offset-of-a-date-object) |
+| 295 | [How do you load CSS and JS files dynamically](#how-do-you-load-css-and-js-files-dynamically) |
+| 296 | [What are the different methods to find HTML elements in DOM](#what-are-the-different-methods-to-find-html-elements-in-dom) |
+| 297 | [What is jQuery](#what-is-jquery) |
+| 298 | [What is V8 JavaScript engine](#what-is-v8-javascript-engine) |
+| 299 | [Why do we call javascript as dynamic language](#why-do-we-call-javascript-as-dynamic-language) |
+| 300 | [What is a void operator](#what-is-a-void-operator) |
+| 301 | [How to set the cursor to wait](#how-to-set-the-cursor-to-wait) |
+| 302 | [How do you create an infinite loop](#how-do-you-create-an-infinite-loop) |
+| 303 | [Why do you need to avoid with statement](#why-do-you-need-to-avoid-with-statement) |
+| 304 | [What is the output of the following for loops](#what-is-the-output-of-the-following-for-loops) |
+| 305 | [List down some of the features of ES6](#list-down-some-of-the-features-of-es6) |
+| 306 | [What is ES6](#what-is-es6) |
+| 307 | [Can I redeclare let and const variables](#can-i-redeclare-let-and-const-variables) |
+| 308 | [Does the `const` variable make the value immutable](#does-the-const-variable-make-the-value-immutable) |
+| 309 | [What are default parameters](#what-are-default-parameters) |
+| 310 | [What are template literals](#what-are-template-literals) |
+| 311 | [How do you write multi-line strings in template literals](#how-do-you-write-multi-line-strings-in-template-literals) |
+| 312 | [What are nesting templates](#what-are-nesting-templates) |
+| 313 | [What are tagged templates](#what-are-tagged-templates) |
+| 314 | [What are raw strings](#what-are-raw-strings) |
+| 315 | [What is destructuring assignment](#what-is-destructuring-assignment) |
+| 316 | [What are default values in destructuring assignment](#what-are-default-values-in-destructuring-assignment) |
+| 317 | [How do you swap variables in destructuring assignment](#how-do-you-swap-variables-in-destructuring-assignment) |
+| 318 | [What are enhanced object literals](#what-are-enhanced-object-literals) |
+| 319 | [What are dynamic imports](#what-are-dynamic-imports) |
+| 320 | [What are the use cases for dynamic imports](#what-are-the-use-cases-for-dynamic-imports) |
+| 321 | [What are typed arrays](#what-are-typed-arrays) |
+| 322 | [What are the advantages of module loaders](#what-are-the-advantages-of-module-loaders) |
+| 323 | [What is collation](#what-is-collation) |
+| 324 | [What is for...of statement](#what-is-forof-statement) |
+| 325 | [What is the output of below spread operator array](#what-is-the-output-of-below-spread-operator-array) |
+| 326 | [Is PostMessage secure](#is-postmessage-secure) |
+| 327 | [What are the problems with postmessage target origin as wildcard](#what-are-the-problems-with-postmessage-target-origin-as-wildcard) |
+| 328 | [How do you avoid receiving postMessages from attackers](#how-do-you-avoid-receiving-postmessages-from-attackers) |
+| 329 | [Can I avoid using postMessages completely](#can-i-avoid-using-postmessages-completely) |
+| 330 | [Is postMessages synchronous](#is-postmessages-synchronous) |
+| 331 | [What paradigm is Javascript](#what-paradigm-is-javascript) |
+| 332 | [What is the difference between internal and external javascript](#what-is-the-difference-between-internal-and-external-javascript) |
+| 333 | [Is JavaScript faster than server side script](#is-javascript-faster-than-server-side-script) |
+| 334 | [How do you get the status of a checkbox](#how-do-you-get-the-status-of-a-checkbox) |
+| 335 | [What is the purpose of double tilde operator](#what-is-the-purpose-of-double-tilde-operator) |
+| 336 | [How do you convert character to ASCII code](#how-do-you-convert-character-to-ascii-code) |
+| 337 | [What is ArrayBuffer](#what-is-arraybuffer) |
+| 338 | [What is the output of below string expression](#what-is-the-output-of-below-string-expression) |
+| 339 | [What is the purpose of Error object](#what-is-the-purpose-of-error-object) |
+| 340 | [What is the purpose of EvalError object](#what-is-the-purpose-of-evalerror-object) |
+| 341 | [What are the list of cases error thrown from non-strict mode to strict mode](#what-are-the-list-of-cases-error-thrown-from-non-strict-mode-to-strict-mode) |
+| 342 | [Do all objects have prototypes](#do-all-objects-have-prototypes) |
+| 343 | [What is the difference between a parameter and an argument](#what-is-the-difference-between-a-parameter-and-an-argument) |
+| 344 | [What is the purpose of some method in arrays](#what-is-the-purpose-of-some-method-in-arrays) |
+| 345 | [How do you combine two or more arrays](#how-do-you-combine-two-or-more-arrays) |
+| 346 | [What is the difference between Shallow and Deep copy](#what-is-the-difference-between-shallow-and-deep-copy) |
+| 347 | [How do you create specific number of copies of a string](#how-do-you-create-specific-number-of-copies-of-a-string) |
+| 348 | [How do you return all matching strings against a regular expression](#how-do-you-return-all-matching-strings-against-a-regular-expression) |
+| 349 | [How do you trim a string at the beginning or ending](#how-do-you-trim-a-string-at-the-beginning-or-ending) |
+| 350 | [What is the output of below console statement with unary operator](#what-is-the-output-of-below-console-statement-with-unary-operator) |
+| 351 | [Does javascript uses mixins](#does-javascript-uses-mixins) |
+| 352 | [Mixin Example using Object composition](#mixin-example-using-object-composition) |
+| 353 | [Benefits](#benefits) |
+| 354 | [What is a thunk function](#what-is-a-thunk-function) |
+| 355 | [What are asynchronous thunks](#what-are-asynchronous-thunks) |
+| 356 | [What is the output of below function calls](#what-is-the-output-of-below-function-calls) |
+| 357 | [How to remove all line breaks from a string](#how-to-remove-all-line-breaks-from-a-string) |
+| 358 | [What is the difference between reflow and repaint](#what-is-the-difference-between-reflow-and-repaint) |
+| 359 | [What happens with negating an array](#what-happens-with-negating-an-array) |
+| 360 | [What happens if we add two arrays](#what-happens-if-we-add-two-arrays) |
+| 361 | [What is the output of prepend additive operator on falsy values](#what-is-the-output-of-prepend-additive-operator-on-falsy-values) |
+| 362 | [How do you create self string using special characters](#how-do-you-create-self-string-using-special-characters) |
+| 363 | [How do you remove falsy values from an array](#how-do-you-remove-falsy-values-from-an-array) |
+| 364 | [How do you get unique values of an array](#how-do-you-get-unique-values-of-an-array) |
+| 365 | [What is destructuring aliases](#what-is-destructuring-aliases) |
+| 366 | [How do you map the array values without using map method](#how-do-you-map-the-array-values-without-using-map-method) |
+| 367 | [How do you empty an array](#how-do-you-empty-an-array) |
+| 368 | [How do you round numbers to certain decimals](#how-do-you-round-numbers-to-certain-decimals) |
+| 369 | [What is the easiest way to convert an array to an object](#what-is-the-easiest-way-to-convert-an-array-to-an-object) |
+| 370 | [How do you create an array with some data](#how-do-you-create-an-array-with-some-data) |
+| 371 | [What are the placeholders from console object](#what-are-the-placeholders-from-console-object) |
+| 372 | [Is it possible to add CSS to console messages](#is-it-possible-to-add-css-to-console-messages) |
+| 373 | [What is the purpose of dir method of console object](#what-is-the-purpose-of-dir-method-of-console-object) |
+| 374 | [Is it possible to debug HTML elements in console](#is-it-possible-to-debug-html-elements-in-console) |
+| 375 | [How do you display data in a tabular format using console object](#how-do-you-display-data-in-a-tabular-format-using-console-object) |
+| 376 | [How do you verify that an argument is a Number or not](#how-do-you-verify-that-an-argument-is-a-number-or-not) |
+| 377 | [How do you create copy to clipboard button](#how-do-you-create-copy-to-clipboard-button) |
+| 378 | [What is the shortcut to get timestamp](#what-is-the-shortcut-to-get-timestamp) |
+| 379 | [How do you flattening multi dimensional arrays](#how-do-you-flattening-multi-dimensional-arrays) |
+| 380 | [What is the easiest multi condition checking](#what-is-the-easiest-multi-condition-checking) |
+| 381 | [How do you capture browser back button](#how-do-you-capture-browser-back-button) |
+| 382 | [How do you disable right click in the web page](#how-do-you-disable-right-click-in-the-web-page) |
+| 383 | [What are wrapper objects](#what-are-wrapper-objects) |
+| 384 | [What is AJAX](#what-is-ajax) |
+| 385 | [What are the different ways to deal with Asynchronous Code](#what-are-the-different-ways-to-deal-with-asynchronous-code) |
+| 386 | [How to cancel a fetch request](#how-to-cancel-a-fetch-request) |
+| 387 | [What is web speech API](#what-is-web-speech-api) |
+| 388 | [What is minimum timeout throttling](#what-is-minimum-timeout-throttling) |
+| 389 | [How do you implement zero timeout in modern browsers](#how-do-you-implement-zero-timeout-in-modern-browsers) |
+| 390 | [What are tasks in event loop](#what-are-tasks-in-event-loop) |
+| 391 | [What is microtask](#what-is-microtask) |
+| 392 | [What are different event loops](#what-are-different-event-loops) |
+| 393 | [What is the purpose of queueMicrotask](#what-is-the-purpose-of-queuemicrotask) |
+| 394 | [How do you use javascript libraries in typescript file](#how-do-you-use-javascript-libraries-in-typescript-file) |
+| 395 | [What are the differences between promises and observables](#what-are-the-differences-between-promises-and-observables) |
+| 396 | [What is heap](#what-is-heap) |
+| 397 | [What is an event table](#what-is-an-event-table) |
+| 398 | [What is a microTask queue](#what-is-a-microtask-queue) |
+| 399 | [What is the difference between shim and polyfill](#what-is-the-difference-between-shim-and-polyfill) |
+| 400 | [How do you detect primitive or non primitive value type](#how-do-you-detect-primitive-or-non-primitive-value-type) |
+| 401 | [What is babel](#what-is-babel) |
+| 402 | [Is Node.js completely single threaded](#is-nodejs-completely-single-threaded) |
+| 403 | [What are the common use cases of observables](#what-are-the-common-use-cases-of-observables) |
+| 404 | [What is RxJS](#what-is-rxjs) |
| 405 | [What is the difference between Function constructor and function declaration](#what-is-the-difference-between-function-constructor-and-function-declaration) |
-| 406 | [What is a Short circuit condition](#what-is-a-short-circuit-condition) |
-| 407 | [What is the easiest way to resize an array](#what-is-the-easiest-way-to-resize-an-array) |
-| 408 | [What is an observable](#what-is-an-observable) |
-| 409 | [What is the difference between function and class declarations](#what-is-the-difference-between-function-and-class-declarations) |
-| 410 | [What is an async function](#what-is-an-async-function) |
-| 411 | [How do you prevent promises swallowing errors](#how-do-you-prevent-promises-swallowing-errors) |
-| 412 | [What is deno](#what-is-deno) |
-| 413 | [How do you make an object iterable in javascript](#how-do-you-make-an-object-iterable-in-javascript) |
-| 414 | [What is a Proper Tail Call](#what-is-a-proper-tail-call) |
-| 415 | [How do you check an object is a promise or not](#how-do-you-check-an-object-is-a-promise-or-not) |
-| 416 | [How to detect if a function is called as constructor](#how-to-detect-if-a-function-is-called-as-constructor) |
-| 417 | [What are the differences between arguments object and rest parameter](#what-are-the-differences-between-arguments-object-and-rest-parameter) |
-| 418 | [What are the differences between spread operator and rest parameter](#what-are-the-differences-between-spread-operator-and-rest-parameter) |
-| 419 | [What are the different kinds of generators](#what-are-the-different-kinds-of-generators) |
-| 420 | [What are the built-in iterables](#what-are-the-built-in-iterables) |
-| 421 | [What are the differences between for...of and for...in statements](#what-are-the-differences-between-forof-and-forin-statements) |
-| 422 | [How do you define instance and non-instance properties](#how-do-you-define-instance-and-non-instance-properties) |
-| 423 | [What is the difference between isNaN and Number.isNaN?](#what-is-the-difference-between-isnan-and-numberisnan) |
-| 424 | [How to invoke an IIFE without any extra brackets?](#how-to-invoke-an-iife-without-any-extra-brackets) |
-| 425 | [Is that possible to use expressions in switch cases?](#is-that-possible-to-use-expressions-in-switch-cases) |
-| 426 | [What is the easiest way to ignore promise errors?](#what-is-the-easiest-way-to-ignore-promise-errors) |
-| 427 | [How do style the console output using CSS?](#how-do-style-the-console-output-using-css) |
-| 428 | [What is nullish coalescing operator (??)?](#what-is-nullish-coalescing-operator-) |
-| 429 | [How do you group and nest console output?](#how-do-you-group-and-nest-console-output) |
-| 430 | [What is the difference between dense and sparse arrays?](#what-is-the-difference-between-dense-and-sparse-arrays) |
-| 431 | [What are the different ways to create sparse arrays?](#what-are-the-different-ways-to-create-sparse-arrays) |
-| 432 | [What is the difference between setTimeout, setImmediate and process.nextTick?](#what-is-the-difference-between-settimeout-setimmediate-and-processnexttick) |
-| 433 | [How do you reverse an array without modifying original array?](#how-do-you-reverse-an-array-without-modifying-original-array) |
-| 434 | [How do you create custom HTML element?](#how-do-you-create-custom-html-element) |
-| 435 | [What is global execution context?](#what-is-global-execution-context) |
-| 436 | [What is function execution context?](#what-is-function-execution-context) |
-| 437 | [What is debouncing?](#what-is-debouncing) |
-| 438 | [What is throttling?](#what-is-throttling) |
-| 439 | [What is optional chaining?](#what-is-optional-chaining) |
-| 440 | [What is an environment record?](#what-is-an-environment-record) |
-| 441 | [How to verify if a variable is an array?](#how-to-verify-if-a-variable-is-an-array) |
-| 442 | [What is pass by value and pass by reference?](#what-is-pass-by-value-and-pass-by-reference) |
-| 443 | [What are the differences between primitives and non-primitives?](#what-are-the-differences-between-primitives-and-non-primitives) |
-| 444 | [How do you create your own bind method using either call or apply method?](#how-do-you-create-your-own-bind-method-using-either-call-or-apply-method) |
-| 445 | [What are the differences between pure and impure functions?](#what-are-the-differences-between-pure-and-impure-functions) |
-| 446 | [What is referential transparency?](#what-is-referential-transparency) |
-| 447 | [What are the possible side-effects in javascript?](#what-are-the-possible-side-effects-in-javascript) |
-| 448 | [What are compose and pipe functions?](#what-are-compose-and-pipe-functions) |
-| 449 | [What is module pattern?](#what-is-module-pattern) |
-| 450 | [What is Function Composition?](#what-is-function-composition) |
-| 451 | [How to use await outside of async function prior to ES2022?](#how-to-use-await-outside-of-async-function-prior-to-es2022) |
-| 452 | [What is the purpose of the this keyword in JavaScript?](#what-is-the-purpose-of-the-this-keyword-in-javascript) |
-| 453 | [What are the uses of closures?](#what-are-the-uses-of-closures) |
-| 454 | [What are the phases of execution context?](#what-are-the-phases-of-execution-context) |
-| 455 | [What are the possible reasons for memory leaks?](#what-are-the-possible-reasons-for-memory-leaks) |
-| 456 | [What are the optimization techniques of V8 engine?](#what-are-the-optimization-techniques-of-v8-engine) |
-| 457 | [What are the examples of built-in higher order functions?](#what-are-the-examples-of-built-in-higher-order-functions) |
-| 458 | [What are the benefits higher order functions?](#what-are-the-benefits-higher-order-functions) |
-| 459 | [How do you create polyfills for map, filter and reduce methods?](#how-do-you-create-polyfills-for-map-filter-and-reduce-methods) |
-| 460 | [What is the difference between map and forEach functions?](#what-is-the-difference-between-map-and-foreach-functions) |
-| 461 | [Give an example of statements affected by automatic semicolon insertion?](#give-an-example-of-statements-affected-by-automatic-semicolon-insertion) |
-| 462 | [What are the event phases of a browser?](#what-are-the-event-phases-of-a-browser) |
-| 463 | [What are the real world use cases of proxy?](#what-are-the-real-world-use-cases-of-proxy) |
-| 464 | [What are hidden classes?](#what-are-hidden-classes) |
-| 465 | [What is inline caching?](#what-is-inline-caching) |
-| 466 | [What are the different ways to execute external scripts?](#what-are-the-different-ways-to-execute-external-scripts) |
-| 467 | [What is Lexical Scope?](#what-is-lexical-scope) |
-| 468 | [How to detect system dark mode in javascript?](#how-to-detect-system-dark-mode-in-javascript) |
-| 469 | [What is the purpose of requestAnimationFrame method?](#what-is-the-purpose-of-requestanimationframe-method) |
-| 470 | [What is the difference between substring and substr methods?](#what-is-the-difference-between-substring-and-substr-methods) |
-| 471 | [How to find the number of parameters expected by a function?](#how-to-find-the-number-of-parameters-expected-by-a-function) |
-| 472 | [What is globalThis, and what is the importance of it?](#what-is-globalthis-and-what-is-the-importance-of-it) |
-| 473 | [What are the array mutation methods?](#what-are-the-array-mutation-methods) |
-| 474 | [What is module scope in JavaScript?](#what-is-module-scope-in-javascript) |
-| 475 | [What are shadowing and illegal shadowing?](#what-are-shadowing-and-illegal-shadowing) |
-| 476 | [Why is it important to remove event listeners after use?](#why-is-it-important-to-remove-event-listeners-after-use) |
+| 406 | [What is a Short circuit condition](#what-is-a-short-circuit-condition) |
+| 407 | [What is the easiest way to resize an array](#what-is-the-easiest-way-to-resize-an-array) |
+| 408 | [What is an observable](#what-is-an-observable) |
+| 409 | [What is the difference between function and class declarations](#what-is-the-difference-between-function-and-class-declarations) |
+| 410 | [What is an async function](#what-is-an-async-function) |
+| 411 | [How do you prevent promises swallowing errors](#how-do-you-prevent-promises-swallowing-errors) |
+| 412 | [What is deno](#what-is-deno) |
+| 413 | [How do you make an object iterable in javascript](#how-do-you-make-an-object-iterable-in-javascript) |
+| 414 | [What is a Proper Tail Call](#what-is-a-proper-tail-call) |
+| 415 | [How do you check an object is a promise or not](#how-do-you-check-an-object-is-a-promise-or-not) |
+| 416 | [How to detect if a function is called as constructor](#how-to-detect-if-a-function-is-called-as-constructor) |
+| 417 | [What are the differences between arguments object and rest parameter](#what-are-the-differences-between-arguments-object-and-rest-parameter) |
+| 418 | [What are the differences between spread operator and rest parameter](#what-are-the-differences-between-spread-operator-and-rest-parameter) |
+| 419 | [What are the different kinds of generators](#what-are-the-different-kinds-of-generators) |
+| 420 | [What are the built-in iterables](#what-are-the-built-in-iterables) |
+| 421 | [What are the differences between for...of and for...in statements](#what-are-the-differences-between-forof-and-forin-statements) |
+| 422 | [How do you define instance and non-instance properties](#how-do-you-define-instance-and-non-instance-properties) |
+| 423 | [What is the difference between isNaN and Number.isNaN?](#what-is-the-difference-between-isnan-and-numberisnan) |
+| 424 | [How to invoke an IIFE without any extra brackets?](#how-to-invoke-an-iife-without-any-extra-brackets) |
+| 425 | [Is that possible to use expressions in switch cases?](#is-that-possible-to-use-expressions-in-switch-cases) |
+| 426 | [What is the easiest way to ignore promise errors?](#what-is-the-easiest-way-to-ignore-promise-errors) |
+| 427 | [How do style the console output using CSS?](#how-do-style-the-console-output-using-css) |
+| 428 | [What is nullish coalescing operator (??)?](#what-is-nullish-coalescing-operator-) |
+| 429 | [How do you group and nest console output?](#how-do-you-group-and-nest-console-output) |
+| 430 | [What is the difference between dense and sparse arrays?](#what-is-the-difference-between-dense-and-sparse-arrays) |
+| 431 | [What are the different ways to create sparse arrays?](#what-are-the-different-ways-to-create-sparse-arrays) |
+| 432 | [What is the difference between setTimeout, setImmediate and process.nextTick?](#what-is-the-difference-between-settimeout-setimmediate-and-processnexttick) |
+| 433 | [How do you reverse an array without modifying original array?](#how-do-you-reverse-an-array-without-modifying-original-array) |
+| 434 | [How do you create custom HTML element?](#how-do-you-create-custom-html-element) |
+| 435 | [What is global execution context?](#what-is-global-execution-context) |
+| 436 | [What is function execution context?](#what-is-function-execution-context) |
+| 437 | [What is debouncing?](#what-is-debouncing) |
+| 438 | [What is throttling?](#what-is-throttling) |
+| 439 | [What is optional chaining?](#what-is-optional-chaining) |
+| 440 | [What is an environment record?](#what-is-an-environment-record) |
+| 441 | [How to verify if a variable is an array?](#how-to-verify-if-a-variable-is-an-array) |
+| 442 | [What is pass by value and pass by reference?](#what-is-pass-by-value-and-pass-by-reference) |
+| 443 | [What are the differences between primitives and non-primitives?](#what-are-the-differences-between-primitives-and-non-primitives) |
+| 444 | [How do you create your own bind method using either call or apply method?](#how-do-you-create-your-own-bind-method-using-either-call-or-apply-method) |
+| 445 | [What are the differences between pure and impure functions?](#what-are-the-differences-between-pure-and-impure-functions) |
+| 446 | [What is referential transparency?](#what-is-referential-transparency) |
+| 447 | [What are the possible side-effects in javascript?](#what-are-the-possible-side-effects-in-javascript) |
+| 448 | [What are compose and pipe functions?](#what-are-compose-and-pipe-functions) |
+| 449 | [What is module pattern?](#what-is-module-pattern) |
+| 450 | [What is Function Composition?](#what-is-function-composition) |
+| 451 | [How to use await outside of async function prior to ES2022?](#how-to-use-await-outside-of-async-function-prior-to-es2022) |
+| 452 | [What is the purpose of the this keyword in JavaScript?](#what-is-the-purpose-of-the-this-keyword-in-javascript) |
+| 453 | [What are the uses of closures?](#what-are-the-uses-of-closures) |
+| 454 | [What are the phases of execution context?](#what-are-the-phases-of-execution-context) |
+| 455 | [What are the possible reasons for memory leaks?](#what-are-the-possible-reasons-for-memory-leaks) |
+| 456 | [What are the optimization techniques of V8 engine?](#what-are-the-optimization-techniques-of-v8-engine) |
+| 457 | [What are the examples of built-in higher order functions?](#what-are-the-examples-of-built-in-higher-order-functions) |
+| 458 | [What are the benefits higher order functions?](#what-are-the-benefits-higher-order-functions) |
+| 459 | [How do you create polyfills for map, filter and reduce methods?](#how-do-you-create-polyfills-for-map-filter-and-reduce-methods) |
+| 460 | [What is the difference between map and forEach functions?](#what-is-the-difference-between-map-and-foreach-functions) |
+| 461 | [Give an example of statements affected by automatic semicolon insertion?](#give-an-example-of-statements-affected-by-automatic-semicolon-insertion) |
+| 462 | [What are the event phases of a browser?](#what-are-the-event-phases-of-a-browser) |
+| 463 | [What are the real world use cases of proxy?](#what-are-the-real-world-use-cases-of-proxy) |
+| 464 | [What are hidden classes?](#what-are-hidden-classes) |
+| 465 | [What is inline caching?](#what-is-inline-caching) |
+| 466 | [What are the different ways to execute external scripts?](#what-are-the-different-ways-to-execute-external-scripts) |
+| 467 | [What is Lexical Scope?](#what-is-lexical-scope) |
+| 468 | [How to detect system dark mode in javascript?](#how-to-detect-system-dark-mode-in-javascript) |
+| 469 | [What is the purpose of requestAnimationFrame method?](#what-is-the-purpose-of-requestanimationframe-method) |
+| 470 | [What is the difference between substring and substr methods?](#what-is-the-difference-between-substring-and-substr-methods) |
+| 471 | [How to find the number of parameters expected by a function?](#how-to-find-the-number-of-parameters-expected-by-a-function) |
+| 472 | [What is globalThis, and what is the importance of it?](#what-is-globalthis-and-what-is-the-importance-of-it) |
+| 473 | [What are the array mutation methods?](#what-are-the-array-mutation-methods) |
+| 474 | [What is module scope in JavaScript?](#what-is-module-scope-in-javascript) |
+| 475 | [What are shadowing and illegal shadowing?](#what-are-shadowing-and-illegal-shadowing) |
+| 476 | [Why is it important to remove event listeners after use?](#why-is-it-important-to-remove-event-listeners-after-use) |
+
1. ### What are the possible ways to create objects in JavaScript
- There are many ways to create objects in javascript as mentioned below:
+ There are many ways to create objects in javascript as mentioned below:
- 1. **Object literal syntax:**
+ 1. **Object literal syntax:**
- The object literal syntax (or object initializer), is a comma-separated set of name-value pairs wrapped in curly braces.
+ The object literal syntax (or object initializer), is a comma-separated set of name-value pairs wrapped in curly braces.
- ```javascript
- var object = {
- name: "Sudheer",
- age: 34,
- };
- ```
+ ```javascript
+ var object = {
+ name: "Sudheer",
+ age: 34,
+ };
+ ```
+
+ Object literal property values can be of any data type, including array, function, and nested object.
- Object literal property values can be of any data type, including array, function, and nested object.
+ **Note:** This is one of the easiest ways to create an object and it's most commonly used for creating simple, ad-hoc objects.
- **Note:** This is one of the easiest ways to create an object and it's most commonly used for creating simple, ad-hoc objects.
+ 2. **Object constructor:**
- 2. **Object constructor:**
+ The simplest way to create an empty object is using the `Object` constructor. Currently this approach is not recommended.
- The simplest way to create an empty object is using the `Object` constructor. Currently this approach is not recommended.
+ ```javascript
+ var object = new Object();
+ ```
- ```javascript
- var object = new Object();
- ```
+ The `Object()` is a built-in constructor function so "new" keyword is not required for creating plain objects. The above code snippet can be re-written as:
- The `Object()` is a built-in constructor function so "new" keyword is not required for creating plain objects. The above code snippet can be re-written as:
+ ```javascript
+ var object = Object();
+ ```
- ```javascript
- var object = Object();
- ```
- However, `Object()` can be used to either create a plain object or convert a given value into its corresponding object wrapper, whereas `new Object()` is specifically used to explicitly create a new object instance.
-
- 3. **Object's create method:**
+ However, `Object()` can be used to either create a plain object or convert a given value into its corresponding object wrapper, whereas `new Object()` is specifically used to explicitly create a new object instance.
- The `create` method of Object is used to create a new object by passing the specified prototype object and properties as arguments, i.e., this pattern is helpful to create new objects based on existing objects. In other words, this is useful for setting up **prototypal inheritance**. The second argument is optional and it is used to create properties on a newly created object.
+ 3. **Object's create method:**
- The following code creates a new empty object whose prototype is null.
+ The `create` method of Object is used to create a new object by passing the specified prototype object and properties as arguments, i.e., this pattern is helpful to create new objects based on existing objects. In other words, this is useful for setting up **prototypal inheritance**. The second argument is optional and it is used to create properties on a newly created object.
- ```javascript
- var object = Object.create(null);
- ```
+ The following code creates a new empty object whose prototype is null.
- The following example creates an object along with additional new properties.
+ ```javascript
+ var object = Object.create(null);
+ ```
- ```javascript
- let vehicle = {
- wheels: "4",
- fuelType: "Gasoline",
- color: "Green",
- };
- let carProps = {
- type: {
- value: "Volkswagen",
- },
- model: {
- value: "Golf",
- },
- };
+ The following example creates an object along with additional new properties.
- var car = Object.create(vehicle, carProps);
- console.log(car);
- ```
+ ```javascript
+ let vehicle = {
+ wheels: "4",
+ fuelType: "Gasoline",
+ color: "Green",
+ };
+ let carProps = {
+ type: {
+ value: "Volkswagen",
+ },
+ model: {
+ value: "Golf",
+ },
+ };
- 4. **Function constructor:**
+ var car = Object.create(vehicle, carProps);
+ console.log(car);
+ ```
- In this approach, create any function and apply the new operator to create object instances. This was the main way to do constructor-based OOP before ES6 classes.
+ 4. **Function constructor:**
- ```javascript
- function Person(name) {
- this.name = name;
- this.age = 21;
- }
- var object = new Person("Sudheer");
- ```
- 5. **Function constructor with prototype:**
+ In this approach, create any function and apply the new operator to create object instances. This was the main way to do constructor-based OOP before ES6 classes.
- This is similar to function constructor but it uses prototype for their properties and methods. Using prototype means you're sharing methods/properties across instances, which saves memory and improve performance.
+ ```javascript
+ function Person(name) {
+ this.name = name;
+ this.age = 21;
+ }
+ var object = new Person("Sudheer");
+ ```
+
+ 5. **Function constructor with prototype:**
- ```javascript
- function Person() {}
- Person.prototype.name = "Sudheer";
- var object = new Person();
- ```
+ This is similar to function constructor but it uses prototype for their properties and methods. Using prototype means you're sharing methods/properties across instances, which saves memory and improve performance.
- This is equivalent to creating an instance with `Object.create` method with a function prototype and then calling that function with an instance and parameters as arguments.
+ ```javascript
+ function Person() {}
+ Person.prototype.name = "Sudheer";
+ var object = new Person();
+ ```
- ```javascript
- function func(x, y, z) {
+ This is equivalent to creating an instance with `Object.create` method with a function prototype and then calling that function with an instance and parameters as arguments.
+
+ ```javascript
+ function func(x, y, z) {
this.x = x;
this.y = y;
this.z = z;
- }
+ }
- var instance = new func(1, 2, 3);
- ```
+ var instance = new func(1, 2, 3);
+ ```
- **(OR)**
+ **(OR)**
- ```javascript
- function func(x, y, z) {
- this.x = x;
- this.y = y;
- this.z = z;
- }
- // Create a new instance using function prototype.
- var newInstance = Object.create(func.prototype)
+ ```javascript
+ function func(x, y, z) {
+ this.x = x;
+ this.y = y;
+ this.z = z;
+ }
+ // Create a new instance using function prototype.
+ var newInstance = Object.create(func.prototype)
- // Call the function
- var result = func.call(newInstance, 1, 2, 3),
+ // Call the function
+ var result = func.call(newInstance, 1, 2, 3),
- // If the result is a non-null object then use it otherwise just use the new instance.
- console.log(result && typeof result === 'object' ? result : newInstance);
- ```
+ // If the result is a non-null object then use it otherwise just use the new instance.
+ console.log(result && typeof result === 'object' ? result : newInstance);
+ ```
- 6. **Object's assign method:**
+ 6. **Object's assign method:**
- The `Object.assign` method is used to copy all the properties from one or more source objects and stores them into a target object. This is mainly used for cloning and merging
+ The `Object.assign` method is used to copy all the properties from one or more source objects and stores them into a target object. This is mainly used for cloning and merging
- The following code creates a new staff object by copying properties of his working company and the car he owns.
+ The following code creates a new staff object by copying properties of his working company and the car he owns.
- ```javascript
- const orgObject = { company: "XYZ Corp" };
- const carObject = { name: "Toyota" };
- const staff = Object.assign({}, orgObject, carObject);
- ```
+ ```javascript
+ const orgObject = { company: "XYZ Corp" };
+ const carObject = { name: "Toyota" };
+ const staff = Object.assign({}, orgObject, carObject);
+ ```
- 7. **ES6 Class syntax:**
+ 7. **ES6 Class syntax:**
- ES6 introduces class feature to create objects. This is syntactic sugar over the prototype-based system.
+ ES6 introduces class feature to create objects. This is syntactic sugar over the prototype-based system.
- ```javascript
- class Person {
- constructor(name) {
- this.name = name;
- }
- }
+ ```javascript
+ class Person {
+ constructor(name) {
+ this.name = name;
+ }
+ }
+
+ var object = new Person("Sudheer");
+ ```
- var object = new Person("Sudheer");
- ```
+ 8. **Singleton pattern:**
- 8. **Singleton pattern:**
+ A Singleton is an object which can only be instantiated one time. Repeated calls to its constructor return the same instance. This way one can ensure that they don't accidentally create multiple instances.
- A Singleton is an object which can only be instantiated one time. Repeated calls to its constructor return the same instance. This way one can ensure that they don't accidentally create multiple instances.
+ ##### Singleton with Closure (Classic JS Pattern)
- ##### Singleton with Closure (Classic JS Pattern)
- ```javascript
- const Singleton = (function () {
+ ```javascript
+ const Singleton = (function () {
let instance;
function createInstance() {
@@ -677,337 +682,378 @@
instance = createInstance();
}
return instance;
- }
+ },
};
- })();
+ })();
- // Usage
- const obj1 = Singleton.getInstance();
- const obj2 = Singleton.getInstance();
+ // Usage
+ const obj1 = Singleton.getInstance();
+ const obj2 = Singleton.getInstance();
- console.log(obj1 === obj2); // true
- ```
- In modern JavaScript applications, singletons are commonly implemented using ES6 modules for their built-in caching behavior, or closures for encapsulated state management.
+ console.log(obj1 === obj2); // true
+ ```
+
+ In modern JavaScript applications, singletons are commonly implemented using ES6 modules for their built-in caching behavior, or closures for encapsulated state management.
**[⬆ Back to Top](#table-of-contents)**
2. ### What is a prototype chain
- The prototype chain is a core concept in JavaScript’s inheritance model. It allows objects to inherit properties and methods from other objects. When you try to access a property or method on an object, JavaScript first looks for it on that object itself. If it’s not found, the engine looks up the object's internal `[[Prototype]]` reference (accessible via `Object.getPrototypeOf(obj)` or the deprecated `__proto__` property) and continues searching up the chain until it finds the property or reaches the end (usually `null`).
+ The prototype chain is a core concept in JavaScript’s inheritance model. It allows objects to inherit properties and methods from other objects. When you try to access a property or method on an object, JavaScript first looks for it on that object itself. If it’s not found, the engine looks up the object's internal `[[Prototype]]` reference (accessible via `Object.getPrototypeOf(obj)` or the deprecated `__proto__` property) and continues searching up the chain until it finds the property or reaches the end (usually `null`).
- For objects created via constructor functions, the prototype chain starts with the instance, then refers to the constructor’s `.prototype` object, and continues from there. For example:
+ For objects created via constructor functions, the prototype chain starts with the instance, then refers to the constructor’s `.prototype` object, and continues from there. For example:
- ```javascript
- function Person() {}
- const person1 = new Person();
+ ```javascript
+ function Person() {}
+ const person1 = new Person();
- console.log(Object.getPrototypeOf(person1) === Person.prototype); // true
- ```
+ console.log(Object.getPrototypeOf(person1) === Person.prototype); // true
+ ```
- This mechanism allows for property and method sharing among objects, enabling code reuse and a form of inheritance.
+ This mechanism allows for property and method sharing among objects, enabling code reuse and a form of inheritance.
- **Summary:**
+ **Summary:**
- * The prototype chain enables inheritance in JavaScript.
- * If a property isn’t found on an object, JavaScript looks up its prototype chain.
- * The prototype of an object instance can be accessed with `Object.getPrototypeOf(obj)` or `__proto__`.
- * The prototype of a constructor function is available via `Constructor.prototype`.
- * The chain ends when the prototype is `null`.
+ - The prototype chain enables inheritance in JavaScript.
+ - If a property isn’t found on an object, JavaScript looks up its prototype chain.
+ - The prototype of an object instance can be accessed with `Object.getPrototypeOf(obj)` or `__proto__`.
+ - The prototype of a constructor function is available via `Constructor.prototype`.
+ - The chain ends when the prototype is `null`.
- The prototype chain among objects appears as below,
-
- 
+ The prototype chain among objects appears as below,
- **[⬆ Back to Top](#table-of-contents)**
+ 
+
+ **[⬆ Back to Top](#table-of-contents)**
3. ### What is the Difference Between `call`, `apply`, and `bind`
- In JavaScript, `call`, `apply`, and `bind` are methods that allow you to control the context (`this` value) in which a function is executed. While their purposes are similar, they differ in how they handle arguments and when the function is invoked.
+In JavaScript, `call`, `apply`, and `bind` are methods that allow you to control the context (`this` value) in which a function is executed. While their purposes are similar, they differ in how they handle arguments and when the function is invoked.
- ---
+---
- #### `call`
+#### `call`
- - **Description:**
- The `call()` method invokes a function immediately, allowing you to specify the value of `this` and pass arguments individually (comma-separated).
+- **Description:**
+ The `call()` method invokes a function immediately, allowing you to specify the value of `this` and pass arguments individually (comma-separated).
- - **Syntax:**
- ```js
- func.call(thisArg, arg1, arg2, ...)
- ```
+- **Syntax:**
- - **Example:**
- ```js
- var employee1 = { firstName: "John", lastName: "Rodson" };
- var employee2 = { firstName: "Jimmy", lastName: "Baily" };
+ ```js
+ func.call(thisArg, arg1, arg2, ...)
+ ```
- function invite(greeting1, greeting2) {
- console.log(
- greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
- );
- }
+- **Example:**
- invite.call(employee1, "Hello", "How are you?"); // Hello John Rodson, How are you?
- invite.call(employee2, "Hello", "How are you?"); // Hello Jimmy Baily, How are you?
- ```
+ ```js
+ var employee1 = { firstName: "John", lastName: "Rodson" };
+ var employee2 = { firstName: "Jimmy", lastName: "Baily" };
- ---
+ function invite(greeting1, greeting2) {
+ console.log(
+ greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
+ );
+ }
- #### `apply`
+ invite.call(employee1, "Hello", "How are you?"); // Hello John Rodson, How are you?
+ invite.call(employee2, "Hello", "How are you?"); // Hello Jimmy Baily, How are you?
+ ```
- - **Description:**
- The `apply()` method is similar to `call()`, but it takes the function arguments as an array (or array-like object) instead of individual arguments.
+---
- - **Syntax:**
- ```js
- func.apply(thisArg, [argsArray])
- ```
+#### `apply`
- - **Example:**
- ```js
- var employee1 = { firstName: "John", lastName: "Rodson" };
- var employee2 = { firstName: "Jimmy", lastName: "Baily" };
+- **Description:**
+ The `apply()` method is similar to `call()`, but it takes the function arguments as an array (or array-like object) instead of individual arguments.
- function invite(greeting1, greeting2) {
- console.log(
- greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
- );
- }
+- **Syntax:**
- invite.apply(employee1, ["Hello", "How are you?"]); // Hello John Rodson, How are you?
- invite.apply(employee2, ["Hello", "How are you?"]); // Hello Jimmy Baily, How are you?
- ```
+ ```js
+ func.apply(thisArg, [argsArray]);
+ ```
- ---
+- **Example:**
- #### `bind`
+ ```js
+ var employee1 = { firstName: "John", lastName: "Rodson" };
+ var employee2 = { firstName: "Jimmy", lastName: "Baily" };
- - **Description:**
- The `bind()` method creates a new function with a specific `this` value and, optionally, preset initial arguments. Unlike `call` and `apply`, `bind` does **not** immediately invoke the function; instead, it returns a new function that you can call later.
+ function invite(greeting1, greeting2) {
+ console.log(
+ greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
+ );
+ }
- - **Syntax:**
- ```js
- var boundFunc = func.bind(thisArg[, arg1[, arg2[, ...]]])
- ```
+ invite.apply(employee1, ["Hello", "How are you?"]); // Hello John Rodson, How are you?
+ invite.apply(employee2, ["Hello", "How are you?"]); // Hello Jimmy Baily, How are you?
+ ```
- - **Example:**
- ```js
- var employee1 = { firstName: "John", lastName: "Rodson" };
- var employee2 = { firstName: "Jimmy", lastName: "Baily" };
+---
- function invite(greeting1, greeting2) {
- console.log(
- greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
- );
- }
+#### `bind`
- var inviteEmployee1 = invite.bind(employee1);
- var inviteEmployee2 = invite.bind(employee2);
+- **Description:**
+ The `bind()` method creates a new function with a specific `this` value and, optionally, preset initial arguments. Unlike `call` and `apply`, `bind` does **not** immediately invoke the function; instead, it returns a new function that you can call later.
- inviteEmployee1("Hello", "How are you?"); // Hello John Rodson, How are you?
- inviteEmployee2("Hello", "How are you?"); // Hello Jimmy Baily, How are you?
- ```
+- **Syntax:**
- ---
+ ```js
+ var boundFunc = func.bind(thisArg[, arg1[, arg2[, ...]]])
+ ```
+
+- **Example:**
- #### Summary
+ ```js
+ var employee1 = { firstName: "John", lastName: "Rodson" };
+ var employee2 = { firstName: "Jimmy", lastName: "Baily" };
+
+ function invite(greeting1, greeting2) {
+ console.log(
+ greeting1 + " " + this.firstName + " " + this.lastName + ", " + greeting2
+ );
+ }
- | Method | Invokes Function Immediately? | How Arguments Are Passed | Returns |
- |--------|-------------------------------|----------------------------------|--------------|
- | `call` | Yes | Comma-separated list | Function's result |
- | `apply`| Yes | Array or array-like object | Function's result |
- | `bind` | No | (Optional) preset, then rest | New function |
+ var inviteEmployee1 = invite.bind(employee1);
+ var inviteEmployee2 = invite.bind(employee2);
- ---
+ inviteEmployee1("Hello", "How are you?"); // Hello John Rodson, How are you?
+ inviteEmployee2("Hello", "How are you?"); // Hello Jimmy Baily, How are you?
+ ```
- ## Key Points
+---
- - **`call`** and **`apply`** are almost interchangeable; both invoke the function immediately, but differ in how arguments are passed.
- - _Tip:_ "Call is for Comma-separated, Apply is for Array."
- - **`bind`** does not execute the function immediately. Instead, it creates a new function with the specified `this` value and optional arguments, which can be called later.
+#### Summary
- - Use `call` or `apply` when you want to immediately invoke a function with a specific `this` context. Use `bind` when you want to create a new function with a specific `this` context to be invoked later.
-
- ---
+| Method | Invokes Function Immediately? | How Arguments Are Passed | Returns |
+| ------- | ----------------------------- | ---------------------------- | ----------------- |
+| `call` | Yes | Comma-separated list | Function's result |
+| `apply` | Yes | Array or array-like object | Function's result |
+| `bind` | No | (Optional) preset, then rest | New function |
- **[⬆ Back to Top](#table-of-contents)**
+---
+
+## Key Points
+
+- **`call`** and **`apply`** are almost interchangeable; both invoke the function immediately, but differ in how arguments are passed.
+ - _Tip:_ "Call is for Comma-separated, Apply is for Array."
+- **`bind`** does not execute the function immediately. Instead, it creates a new function with the specified `this` value and optional arguments, which can be called later.
+
+- Use `call` or `apply` when you want to immediately invoke a function with a specific `this` context. Use `bind` when you want to create a new function with a specific `this` context to be invoked later.
+
+---
+
+**[⬆ Back to Top](#table-of-contents)**
4. ### What is JSON and its common operations
- **JSON (JavaScript Object Notation)** is a lightweight, text-based data format that uses JavaScript object syntax for structuring data. It was popularized by Douglas Crockford and is widely used for transmitting data between a server and a client in web applications. JSON files typically have a `.json` extension and use the MIME type `application/json`.
+ **JSON (JavaScript Object Notation)** is a lightweight, text-based data format that uses JavaScript object syntax for structuring data. It was popularized by Douglas Crockford and is widely used for transmitting data between a server and a client in web applications. JSON files typically have a `.json` extension and use the MIME type `application/json`.
- #### Common Operations with JSON
+ #### Common Operations with JSON
- 1. **Parsing**: Transforming a JSON-formatted string into a native JavaScript object.
- ```js
- const obj = JSON.parse(jsonString);
- ```
- - Example:
- ```js
- const jsonString = '{"name":"John","age":30}';
- const obj = JSON.parse(jsonString); // { name: "John", age: 30 }
- ```
+ 1. **Parsing**: Transforming a JSON-formatted string into a native JavaScript object.
- 2. **Stringification**: Converting a JavaScript object into a JSON-formatted string, commonly used for data transmission or storage.
- ```js
- const jsonString = JSON.stringify(object);
- ```
- - Example:
- ```js
- const obj = { name: "Jane", age: 25 };
- const jsonString = JSON.stringify(obj); // '{"name":"Jane","age":25}'
- ```
+ ```js
+ const obj = JSON.parse(jsonString);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ - Example:
+ ```js
+ const jsonString = '{"name":"John","age":30}';
+ const obj = JSON.parse(jsonString); // { name: "John", age: 30 }
+ ```
+
+ 2. **Stringification**: Converting a JavaScript object into a JSON-formatted string, commonly used for data transmission or storage.
+
+ ```js
+ const jsonString = JSON.stringify(object);
+ ```
+
+ - Example:
+ ```js
+ const obj = { name: "Jane", age: 25 };
+ const jsonString = JSON.stringify(obj); // '{"name":"Jane","age":25}'
+ ```
+
+ **[⬆ Back to Top](#table-of-contents)**
5. ### What is the purpose of the array slice method
- The `slice()` method in JavaScript is used to extract a section of an array, returning a new array containing the selected elements. It does not modify the original array. The method takes two arguments:
+ The `slice()` method in JavaScript is used to extract a section of an array, returning a new array containing the selected elements. It does not modify the original array. The method takes two arguments:
- - **start**: The index at which extraction begins (inclusive).
- - **end** (optional): The index before which to end extraction (exclusive). If omitted, extraction continues to the end of the array.
+ - **start**: The index at which extraction begins (inclusive).
+ - **end** (optional): The index before which to end extraction (exclusive). If omitted, extraction continues to the end of the array.
- You can also use negative indices, which count from the end of the array.
+ You can also use negative indices, which count from the end of the array.
- #### Examples:
+ #### Examples:
- ```js
- let arrayIntegers = [1, 2, 3, 4, 5];
+ ```js
+ let arrayIntegers = [1, 2, 3, 4, 5];
- let arrayIntegers1 = arrayIntegers.slice(0, 2); // [1, 2]
- let arrayIntegers2 = arrayIntegers.slice(2, 3); // [3]
- let arrayIntegers3 = arrayIntegers.slice(4); // [5]
- let arrayIntegers4 = arrayIntegers.slice(-3, -1); // [3, 4]
- ```
+ let arrayIntegers1 = arrayIntegers.slice(0, 2); // [1, 2]
+ let arrayIntegers2 = arrayIntegers.slice(2, 3); // [3]
+ let arrayIntegers3 = arrayIntegers.slice(4); // [5]
+ let arrayIntegers4 = arrayIntegers.slice(-3, -1); // [3, 4]
+ ```
- **Note:**
- The `slice()` method does **not** mutate (change) the original array; instead, it returns a new array containing the extracted elements.
+ **Note:**
+ The `slice()` method does **not** mutate (change) the original array; instead, it returns a new array containing the extracted elements.
+ **Important**
+ **Note on Shallow**
+ The `slice()` method performs a shallow copy. This means that for arrays containing objects, it copies the references to those objects rather than duplicating the objects themselves.
+ Therefore, modifying a nested object in the new array will also modify it in the original array, since both arrays reference the same object.
- **[⬆ Back to Top](#table-of-contents)**
+ #### Example:
+
+ ```js
+ let originalUsers = [{ name: "Alice" }, { name: "Bob" }];
+ let slicedUsers = originalUsers.slice(0, 1);
+
+ // Modify the object in the new, sliced array
+ slicedUsers[0].name = "Zelda";
+
+ // The change is reflected in the original array
+ console.log(originalUsers[0].name); // "Zelda"
+ ```
+
+ **Note**:
+ The change occurs because both arrays point to the same object in memory.
+
+ **[⬆ Back to Top](#table-of-contents)**
6. ### What is the purpose of the array splice method
- The `splice()` method in JavaScript is used to add, remove, or replace elements within an array. Unlike `slice()`, which creates a shallow copy and does not alter the original array, `splice()` **modifies the original array in place** and returns an array containing the removed elements.
+ The `splice()` method in JavaScript is used to add, remove, or replace elements within an array. Unlike `slice()`, which creates a shallow copy and does not alter the original array, `splice()` **modifies the original array in place** and returns an array containing the removed elements.
- #### Syntax
+ #### Syntax
- ```javascript
- array.splice(start, deleteCount, item1, item2, ...)
- ```
- - **start:** The index at which to start changing the array.
- - **deleteCount:** (Optional) The number of elements to remove from the array. If omitted, all elements from the start index to the end of the array will be removed.
- - **item1, item2, ...:** (Optional) Elements to add to the array, starting at the start position.
+ ```javascript
+ array.splice(start, deleteCount, item1, item2, ...)
+ ```
- #### Examples
+ - **start:** The index at which to start changing the array.
+ - **deleteCount:** (Optional) The number of elements to remove from the array. If omitted, all elements from the start index to the end of the array will be removed.
+ - **item1, item2, ...:** (Optional) Elements to add to the array, starting at the start position.
- ```javascript
- let arrayIntegersOriginal1 = [1, 2, 3, 4, 5];
- let arrayIntegersOriginal2 = [1, 2, 3, 4, 5];
- let arrayIntegersOriginal3 = [1, 2, 3, 4, 5];
-
- // Remove the first two elements
- let arrayIntegers1 = arrayIntegersOriginal1.splice(0, 2);
- // arrayIntegers1: [1, 2]
- // arrayIntegersOriginal1 (after): [3, 4, 5]
-
- // Remove all elements from index 3 onwards
- let arrayIntegers2 = arrayIntegersOriginal2.splice(3);
- // arrayIntegers2: [4, 5]
- // arrayIntegersOriginal2 (after): [1, 2, 3]
-
- // Remove 1 element at index 3, then insert "a", "b", "c" at that position
- let arrayIntegers3 = arrayIntegersOriginal3.splice(3, 1, "a", "b", "c");
- // arrayIntegers3: [4]
- // arrayIntegersOriginal3 (after): [1, 2, 3, "a", "b", "c", 5]
- ```
+ #### Examples
- **Note:**
- - The `splice()` method **modifies the original array**.
- - It returns an array containing the elements that were removed (if any).
- - You can use it both to remove and insert elements in a single operation.
+ ```javascript
+ let arrayIntegersOriginal1 = [1, 2, 3, 4, 5];
+ let arrayIntegersOriginal2 = [1, 2, 3, 4, 5];
+ let arrayIntegersOriginal3 = [1, 2, 3, 4, 5];
+
+ // Remove the first two elements
+ let arrayIntegers1 = arrayIntegersOriginal1.splice(0, 2);
+ // arrayIntegers1: [1, 2]
+ // arrayIntegersOriginal1 (after): [3, 4, 5]
+
+ // Remove all elements from index 3 onwards
+ let arrayIntegers2 = arrayIntegersOriginal2.splice(3);
+ // arrayIntegers2: [4, 5]
+ // arrayIntegersOriginal2 (after): [1, 2, 3]
+
+ // Remove 1 element at index 3, then insert "a", "b", "c" at that position
+ let arrayIntegers3 = arrayIntegersOriginal3.splice(3, 1, "a", "b", "c");
+ // arrayIntegers3: [4]
+ // arrayIntegersOriginal3 (after): [1, 2, 3, "a", "b", "c", 5]
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **Note:**
+
+ - The `splice()` method **modifies the original array**.
+ - It returns an array containing the elements that were removed (if any).
+ - You can use it both to remove and insert elements in a single operation.
+
+ **[⬆ Back to Top](#table-of-contents)**
7. ### What is the difference between slice and splice
-
- Here are the key differences between `slice()` and `splice()` methods in JavaScript arrays:
- | `slice()` | `splice()` |
- | ------------------------------------------------- | --------------------------------------------------- |
- | Does **not** modify the original array (immutable) | Modifies the original array (mutable) |
- | Returns a **shallow copy** (subset) of selected elements | Returns an array of the **removed** elements |
- | Used to **extract** elements from an array | Used to **add**, **remove**, or **replace** elements in an array |
- | Syntax: `array.slice(start, end)` | Syntax: `array.splice(start, deleteCount, ...items)` |
+ Here are the key differences between `slice()` and `splice()` methods in JavaScript arrays:
- **Summary:**
- - Use `slice()` when you want to copy or extract elements without altering the original array.
- - Use `splice()` when you need to add, remove, or replace elements and want to change the original array.
+ | `slice()` | `splice()` |
+ | ---------------------------------------------------- | ---------------------------------------------------------------- |
+ | Does **not** modify the original array (immutable) | Modifies the original array (mutable) |
+ | Returns a **shallow** copy of elements. | Returns an array of the **removed** elements |
+ | (For objects, references are copied, not the objects | |
+ | themselves.) | |
+ | Used to **extract** elements from an array | Used to **add**, **remove**, or **replace** elements in an array |
+ | Syntax: `array.slice(start, end)` | Syntax: `array.splice(start, deleteCount, ...items)` |
- **[⬆ Back to Top](#table-of-contents)**
+ **Summary:**
+
+ - Use `slice()` when you want to copy or extract elements without altering the original array.
+ - Use `splice()` when you need to add, remove, or replace elements and want to change the original array.
+
+ **[⬆ Back to Top](#table-of-contents)**
8. ### How do you compare Object and Map
- **Objects** and **Maps** both allow you to associate keys with values, retrieve those values, delete keys, and check if a key exists. Historically, Objects have been used as Maps, but there are several key differences that make `Map` a better choice in certain scenarios:
+ **Objects** and **Maps** both allow you to associate keys with values, retrieve those values, delete keys, and check if a key exists. Historically, Objects have been used as Maps, but there are several key differences that make `Map` a better choice in certain scenarios:
- | Feature | Object | Map |
- |--------------------------|-----------------------------------------------------|----------------------------------------------------------|
- | **Key Types** | Only strings and symbols are valid keys | Any value can be used as a key (objects, functions, primitives) |
- | **Key Order** | Keys are unordered (in practice, insertion order is mostly preserved for string keys, but not guaranteed) | Keys are ordered by insertion; iteration follows insertion order |
- | **Size Property** | No built-in way to get the number of keys; must use `Object.keys(obj).length` | Use the `.size` property for the number of entries |
- | **Iterability** | Not directly iterable; must use `Object.keys`, `Object.values`, or `Object.entries` | Directly iterable with `for...of`, `.keys()`, `.values()`, `.entries()` |
- | **Prototype** | Has a prototype chain; may have default properties that can collide with custom keys (can be avoided with `Object.create(null)`) | Does not have a prototype, so there are no default keys |
- | **Performance** | May be less efficient for frequent additions/removals | Optimized for frequent additions and deletions |
- | **Serialization** | Can be easily serialized to JSON | Cannot be directly serialized to JSON |
+ | Feature | Object | Map |
+ | ----------------- | -------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------- |
+ | **Key Types** | Only strings and symbols are valid keys | Any value can be used as a key (objects, functions, primitives) |
+ | **Key Order** | Keys are unordered (in practice, insertion order is mostly preserved for string keys, but not guaranteed) | Keys are ordered by insertion; iteration follows insertion order |
+ | **Size Property** | No built-in way to get the number of keys; must use `Object.keys(obj).length` | Use the `.size` property for the number of entries |
+ | **Iterability** | Not directly iterable; must use `Object.keys`, `Object.values`, or `Object.entries` | Directly iterable with `for...of`, `.keys()`, `.values()`, `.entries()` |
+ | **Prototype** | Has a prototype chain; may have default properties that can collide with custom keys (can be avoided with `Object.create(null)`) | Does not have a prototype, so there are no default keys |
+ | **Performance** | May be less efficient for frequent additions/removals | Optimized for frequent additions and deletions |
+ | **Serialization** | Can be easily serialized to JSON | Cannot be directly serialized to JSON |
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
9. ### What is the difference between == and === operators
- JavaScript provides two types of equality operators:
- - **Loose equality (`==`, `!=`)**: Performs type conversion if the types differ, comparing values after converting them to a common type.
- - **Strict equality (`===`, `!==`)**: Compares both value and type, without any type conversion.
+ JavaScript provides two types of equality operators:
- #### Strict Equality (`===`)
- - Two strings are strictly equal if they have exactly the same sequence of characters and length.
- - Two numbers are strictly equal if they have the same numeric value.
- - **Special cases:**
- - `NaN === NaN` is `false`
- - `+0 === -0` is `true`
- - Two booleans are strictly equal if both are `true` or both are `false`.
- - Two objects are strictly equal if they refer to the **same object** in memory.
- - `null` and `undefined` are **not** strictly equal.
+ - **Loose equality (`==`, `!=`)**: Performs type conversion if the types differ, comparing values after converting them to a common type.
+ - **Strict equality (`===`, `!==`)**: Compares both value and type, without any type conversion.
- #### Loose Equality (`==`)
- - Converts operands to the same type before making the comparison.
- - `null == undefined` is `true`.
- - `"1" == 1` is `true` because the string is converted to a number.
- - `0 == false` is `true` because `false` is converted to `0`.
+ #### Strict Equality (`===`)
- #### Examples:
+ - Two strings are strictly equal if they have exactly the same sequence of characters and length.
+ - Two numbers are strictly equal if they have the same numeric value.
+ - **Special cases:**
+ - `NaN === NaN` is `false`
+ - `+0 === -0` is `true`
+ - Two booleans are strictly equal if both are `true` or both are `false`.
+ - Two objects are strictly equal if they refer to the **same object** in memory.
+ - `null` and `undefined` are **not** strictly equal.
- ```javascript
- 0 == false // true (loose equality, type coercion)
- 0 === false // false (strict equality, different types)
- 1 == "1" // true (string converted to number)
- 1 === "1" // false (different types)
- null == undefined // true (special case)
- null === undefined // false (different types)
- '0' == false // true ('0' is converted to 0)
- '0' === false // false (different types)
- NaN == NaN // false (NaN is never equal to itself)
- NaN === NaN // false
- [] == [] // false (different array objects)
- [] === [] // false
- {} == {} // false (different object references)
- {} === {} // false
- ```
- **[⬆ Back to Top](#table-of-contents)**
+ #### Loose Equality (`==`)
+
+ - Converts operands to the same type before making the comparison.
+ - `null == undefined` is `true`.
+ - `"1" == 1` is `true` because the string is converted to a number.
+ - `0 == false` is `true` because `false` is converted to `0`.
+
+ #### Examples:
+
+ ```javascript
+ 0 == false // true (loose equality, type coercion)
+ 0 === false // false (strict equality, different types)
+ 1 == "1" // true (string converted to number)
+ 1 === "1" // false (different types)
+ null == undefined // true (special case)
+ null === undefined // false (different types)
+ '0' == false // true ('0' is converted to 0)
+ '0' === false // false (different types)
+ NaN == NaN // false (NaN is never equal to itself)
+ NaN === NaN // false
+ [] == [] // false (different array objects)
+ [] === [] // false
+ {} == {} // false (different object references)
+ {} === {} // false
+ ```
+
+ **[⬆ Back to Top](#table-of-contents)**
10. ### What are lambda expressions or arrow functions
**Arrow functions** (also known as "lambda expressions") provide a concise syntax for writing function expressions in JavaScript. Introduced in ES6, arrow functions are often shorter and more readable, especially for simple operations or callbacks.
#### Key Features:
+
- Arrow functions do **not** have their own `this`, `arguments`, `super`, or `new.target` bindings. They inherit these from their surrounding (lexical) context.
- They are best suited for non-method functions, such as callbacks or simple computations.
- Arrow functions **cannot** be used as constructors and do not have a `prototype` property.
@@ -1016,9 +1062,9 @@
#### Syntax Examples:
```javascript
- const arrowFunc1 = (a, b) => a + b; // Multiple parameters, returns a + b
- const arrowFunc2 = a => a * 10; // Single parameter (parentheses optional), returns a * 10
- const arrowFunc3 = () => {}; // No parameters, returns undefined
+ const arrowFunc1 = (a, b) => a + b; // Multiple parameters, returns a + b
+ const arrowFunc2 = (a) => a * 10; // Single parameter (parentheses optional), returns a * 10
+ const arrowFunc3 = () => {}; // No parameters, returns undefined
const arrowFunc4 = (a, b) => {
// Multiple statements require curly braces and explicit return
const sum = a + b;
@@ -1037,7 +1083,7 @@
3. You can return a function from another function.
This capability enables powerful patterns like callbacks, higher-order functions, event handling, and functional programming in JavaScript.
-
+
For example, the handler function below is assigned to a variable and then passed as an argument to the `addEventListener` method.
```javascript
@@ -1049,7 +1095,7 @@
12. ### What is a first order function
- A first-order function is a function that doesn’t accept another function as an argument and doesn’t return a function as its return value. i.e, It's a regular function that works with primitive or non-function values.
+ A first-order function is a function that doesn’t accept another function as an argument and doesn’t return a function as its return value. i.e, It's a regular function that works with primitive or non-function values.
```javascript
const firstOrder = () => console.log("I am a first order function!");
@@ -1063,17 +1109,17 @@
The syntactic structure of higher order function will be explained with an example as follows,
- ```javascript
- // First-order function (does not accept or return another function)
- const firstOrderFunc = () =>
- console.log("Hello, I am a first-order function");
+ ```javascript
+ // First-order function (does not accept or return another function)
+ const firstOrderFunc = () =>
+ console.log("Hello, I am a first-order function");
- // Higher-order function (accepts a function as an argument)
- const higherOrder = (callback) => callback();
+ // Higher-order function (accepts a function as an argument)
+ const higherOrder = (callback) => callback();
- // Passing the first-order function to the higher-order function
- higherOrder(firstOrderFunc);
- ```
+ // Passing the first-order function to the higher-order function
+ higherOrder(firstOrderFunc);
+ ```
In this example:
@@ -1095,6 +1141,7 @@
const unaryFunction = (a) => console.log(a + 10); // This will add 10 to the input and log the result
unaryFunction(5); // Output: 15
```
+
In this example:
- `unaryFunction` takes a single parameter `a`, making it a unary function.
@@ -1103,12 +1150,11 @@
**[⬆ Back to Top](#table-of-contents)**
15. ### What is the currying function
-
+
**Currying** is the process of transforming a function with **multiple arguments** into a sequence of **nested functions**, each accepting **only one argument** at a time.
This concept is named after mathematician **Haskell Curry**, and is commonly used in functional programming to enhance modularity and reuse.
-
## Before Currying (Normal n-ary Function)
```javascript
@@ -1116,27 +1162,30 @@
console.log(multiArgFunction(1, 2, 3)); // Output: 6
```
+
This is a standard function that takes three arguments at once.
## After Currying (Unary Function Chain)
+
```javascript
const curryUnaryFunction = (a) => (b) => (c) => a + b + c;
- console.log(curryUnaryFunction(1)); // Returns: function (b) => ...
- console.log(curryUnaryFunction(1)(2)); // Returns: function (c) => ...
+ console.log(curryUnaryFunction(1)); // Returns: function (b) => ...
+ console.log(curryUnaryFunction(1)(2)); // Returns: function (c) => ...
console.log(curryUnaryFunction(1)(2)(3)); // Output: 6
-
```
+
Each function in the chain accepts one argument and returns the next function, until all arguments are provided and the final result is computed.
## Benefits of Currying
- - Improves code reusability
+
+ - Improves code reusability
→ You can partially apply functions with known arguments.
- - Enhances functional composition
+ - Enhances functional composition
→ Easier to compose small, pure functions.
- - Encourages clean, modular code
+ - Encourages clean, modular code
→ You can split logic into smaller single-responsibility functions.
**[⬆ Back to Top](#table-of-contents)**
@@ -1160,15 +1209,17 @@
// Usage
console.log(impureAddNumber(6)); // returns 1
- console.log(numberArray); // returns [6]
+ console.log(numberArray); // returns [6]
console.log(pureAddNumber(7)(numberArray)); // returns [6, 7]
- console.log(numberArray); // remains [6]
+ console.log(numberArray); // remains [6]
```
+
- `impureAddNumber` changes the external variable numberArray and returns the new length of the array, making it impure.
- `pureAddNumber` creates a new array with the added number and does not modify the original array, making it pure.
17. ### What are the benefits of pure functions
+
Some of the major benefits of pure functions are listed below,
- **Easier testing:** Since output depends only on input, pure functions are simple to test.
@@ -1183,6 +1234,7 @@
The `let` keyword in JavaScript is used to declare a **block-scoped local variable**. This means that variables declared with `let` are only accessible within the block, statement, or expression where they are defined. This is a significant improvement over the older `var` keyword, which is function-scoped (or globally-scoped if declared outside a function), and does not respect block-level scoping.
#### Key Features of `let`:
+
- **Block Scope:** The variable exists only within the nearest enclosing block (e.g., inside an `{}` pair).
- **No Hoisting Issues:** While `let` declarations are hoisted, they are not initialized until the code defining them is executed. Accessing them before declaration results in a ReferenceError (temporal dead zone).
- **No Redeclaration:** The same variable cannot be declared twice in the same scope with `let`.
@@ -1242,7 +1294,7 @@
21. ### How do you redeclare variables in a switch block without an error
When you try to redeclare variables using `let` or `const` in multiple `case` clauses of a `switch` statement, you will get a SyntaxError. This happens because, in JavaScript, all `case` clauses within a `switch` statement share the same block scope. For example:
-
+
```javascript
let counter = 1;
switch (x) {
@@ -1254,9 +1306,9 @@
break;
}
```
-
+
To avoid this error, you can create a new block scope within each `case` clause by wrapping the code in curly braces `{}`. This way, each `let` or `const` declaration is scoped only to that block, and redeclaration errors are avoided:
-
+
```javascript
let counter = 1;
switch (x) {
@@ -1272,26 +1324,26 @@
}
}
```
-
+
That means, to safely redeclare variables in different cases of a switch statement, wrap each case’s code in its own block using curly braces. This ensures each variable declaration is scoped to its specific case block.
-
+
**[⬆ Back to Top](#table-of-contents)**
22. ### What is the Temporal Dead Zone
The **Temporal Dead Zone (TDZ)** refers to the period between the start of a block and the point where a variable declared with `let` or `const` is initialized. During this time, the variable exists in scope but **cannot be accessed**, and attempting to do so results in a `ReferenceError`.
-
+
This behavior is part of **JavaScript's ES6 (ECMAScript 2015)** specification and applies **only to variables declared with `let` and `const`**, not `var`. Variables declared with `var` are **hoisted** and initialized with `undefined`, so accessing them before the declaration does not throw an error, though it can lead to unexpected results.
-
+
#### Example
-
+
```javascript
function someMethod() {
- console.log(counter1); // Output: undefined (due to var hoisting)
- console.log(counter2); // Throws ReferenceError (TDZ for let)
-
- var counter1 = 1;
- let counter2 = 2;
+ console.log(counter1); // Output: undefined (due to var hoisting)
+ console.log(counter2); // Throws ReferenceError (TDZ for let)
+
+ var counter1 = 1;
+ let counter2 = 2;
}
```
@@ -1744,14 +1796,15 @@
**[⬆ Back to Top](#table-of-contents)**
52. ### What is a promise
+
A **Promise** is a JavaScript object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. It acts as a placeholder for a value that may not be available yet but will be resolved in the future.
A Promise can be in one of **three states**:
+
- `pending`: Initial state, neither fulfilled nor rejected.
- `fulfilled`: The operation completed successfully.
- `rejected`: The operation failed (e.g., due to a network error).
-
#### Promise Syntax
```javascript
@@ -1759,7 +1812,9 @@
// Perform async operation
});
```
+
#### Example: Creating and Using a Promise
+
```javascript
const promise = new Promise((resolve, reject) => {
setTimeout(() => {
@@ -1772,11 +1827,12 @@
.catch((error) => console.error(error)) // Handles any rejection
.finally(() => console.log("Done")); // Runs regardless of success or failure
```
+
In the above example:
- * A `Promise` is created to handle an asynchronous operation with `resolve` and `reject` callbacks.
- * The `setTimeout` resolves the promise with a value after 5 seconds.
- * `.then()`, `.catch()`, and `.finally()` are used to handle success, errors, and cleanup respectively.
+ - A `Promise` is created to handle an asynchronous operation with `resolve` and `reject` callbacks.
+ - The `setTimeout` resolves the promise with a value after 5 seconds.
+ - `.then()`, `.catch()`, and `.finally()` are used to handle success, errors, and cleanup respectively.
The action flow of a promise will be as below,
@@ -1785,14 +1841,15 @@
**[⬆ Back to Top](#table-of-contents)**
53. ### Why do you need a promise
+
Promises are **used to handle asynchronous operations**, especially in languages like JavaScript, which often work with non-blocking operations such as network requests, file I/O, and timers. When an operation is asynchronous, it doesn't immediately return a result; instead, it works in the background and provides the result later. Handling this in a clean, organized way can be difficult without a structured approach.
Promises are used to:
- 1. **Handle asynchronous operations**.
- 2. **Provide a cleaner alternative to callbacks**.
- 3. **Avoid callback hell**.
- 4. **Make code more readable and maintainable**.
+ 1. **Handle asynchronous operations**.
+ 2. **Provide a cleaner alternative to callbacks**.
+ 3. **Avoid callback hell**.
+ 4. **Make code more readable and maintainable**.
**[⬆ Back to Top](#table-of-contents)**
@@ -2229,11 +2286,11 @@
b; // Throws runtime error like "Uncaught ReferenceError: b is not defined"
```
+
This can be confusing, because it says `not defined` instead of `not declared` (Chrome)
**[⬆ Back to Top](#table-of-contents)**
-
82. ### What are global variables
Global variables are those that are available throughout the length of the code without any scope. The var keyword is used to declare a local variable but if you omit it then it will become global variable
@@ -2295,28 +2352,28 @@
To handle events during the capturing phase, you need to pass `true` as the third argument to the `addEventListener` method.
- ```javascript
-
-
-
+ ```javascript
+
+
+
-
- // Parent (capturing)
- // Child (bubbling)
- ```
+ // Bubbling phase: child listener (runs after)
+ child.addEventListener("click", function () {
+ console.log("Child (bubbling)");
+ });
+
+ // Parent (capturing)
+ // Child (bubbling)
+ ```
**[⬆ Back to Top](#table-of-contents)**
@@ -2349,9 +2406,8 @@
```
Here, at first, the event triggers on the child button. Thereafter it bubbles up and triggers the parent div's event handler.
-
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
89. ### How do you submit a form using JavaScript
@@ -2477,4992 +2533,4987 @@
100. ### Is there any relation between Java and JavaScript
- No, they are entirely two different programming languages and have nothing to do with each other. But both of them are Object Oriented Programming languages and like many other languages, they follow similar syntax for basic features(if, else, for, switch, break, continue etc).
+ No, they are entirely two different programming languages and have nothing to do with each other. But both of them are Object Oriented Programming languages and like many other languages, they follow similar syntax for basic features(if, else, for, switch, break, continue etc).
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
101. ### What are events
- Events are "things" that happen to HTML elements. When JavaScript is used in HTML pages, JavaScript can `react` on these events. Some of the examples of HTML events are,
+ Events are "things" that happen to HTML elements. When JavaScript is used in HTML pages, JavaScript can `react` on these events. Some of the examples of HTML events are,
- 1. Web page has finished loading
- 2. Input field was changed
- 3. Button was clicked
+ 1. Web page has finished loading
+ 2. Input field was changed
+ 3. Button was clicked
- Let's describe the behavior of click event for button element,
+ Let's describe the behavior of click event for button element,
- ```javascript
-
-
-
-
-
-
-
-
-
- ```
+ ```javascript
+
+
+
+
+
+
+
+
+
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
102. ### Who created javascript
- JavaScript was created by Brendan Eich in 1995 during his time at Netscape Communications. Initially it was developed under the name `Mocha`, but later the language was officially called `LiveScript` when it first shipped in beta releases of Netscape.
+ JavaScript was created by Brendan Eich in 1995 during his time at Netscape Communications. Initially it was developed under the name `Mocha`, but later the language was officially called `LiveScript` when it first shipped in beta releases of Netscape.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
103. ### What is the use of preventDefault method
- The preventDefault() method cancels the event if it is cancelable, meaning that the default action or behaviour that belongs to the event will not occur. For example, prevent form submission when clicking on submit button and prevent opening the page URL when clicking on hyperlink are some common use cases.
+ The preventDefault() method cancels the event if it is cancelable, meaning that the default action or behaviour that belongs to the event will not occur. For example, prevent form submission when clicking on submit button and prevent opening the page URL when clicking on hyperlink are some common use cases.
- ```javascript
- document
- .getElementById("link")
- .addEventListener("click", function (event) {
- event.preventDefault();
- });
- ```
+ ```javascript
+ document
+ .getElementById("link")
+ .addEventListener("click", function (event) {
+ event.preventDefault();
+ });
+ ```
- **Note:** Remember that not all events are cancelable.
+ **Note:** Remember that not all events are cancelable.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
104. ### What is the use of stopPropagation method
- The stopPropagation method is used to stop the event from bubbling up the event chain. For example, the below nested divs with stopPropagation method prevents default event propagation when clicking on nested div(Div1)
+ The stopPropagation method is used to stop the event from bubbling up the event chain. For example, the below nested divs with stopPropagation method prevents default event propagation when clicking on nested div(Div1)
- ```javascript
-
Click DIV1 Element
-
DIV 2
-
DIV 1
-
-
-
- ```
+
+ ```
+
+ **[⬆ Back to Top](#table-of-contents)**
105. ### What are the steps involved in return false usage
- The return false statement in event handlers performs the below steps,
+ The return false statement in event handlers performs the below steps,
- 1. First it stops the browser's default action or behaviour.
- 2. It prevents the event from propagating the DOM
- 3. Stops callback execution and returns immediately when called.
+ 1. First it stops the browser's default action or behaviour.
+ 2. It prevents the event from propagating the DOM
+ 3. Stops callback execution and returns immediately when called.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
106. ### What is BOM
- The Browser Object Model (BOM) allows JavaScript to "talk to" the browser. It consists of the objects navigator, history, screen, location and document which are children of the window. The Browser Object Model is not standardized and can change based on different browsers.
+ The Browser Object Model (BOM) allows JavaScript to "talk to" the browser. It consists of the objects navigator, history, screen, location and document which are children of the window. The Browser Object Model is not standardized and can change based on different browsers.
- 
+ 
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
107. ### What is the use of setTimeout
- The setTimeout() method is used to call a function or evaluate an expression after a specified number of milliseconds. For example, let's log a message after 2 seconds using setTimeout method,
+ The setTimeout() method is used to call a function or evaluate an expression after a specified number of milliseconds. For example, let's log a message after 2 seconds using setTimeout method,
- ```javascript
- setTimeout(function () {
- console.log("Good morning");
- }, 2000);
- ```
+ ```javascript
+ setTimeout(function () {
+ console.log("Good morning");
+ }, 2000);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
108. ### What is the use of setInterval
- The setInterval() method is used to call a function or evaluate an expression at specified intervals (in milliseconds). For example, let's log a message after 2 seconds using setInterval method,
+ The setInterval() method is used to call a function or evaluate an expression at specified intervals (in milliseconds). For example, let's log a message after 2 seconds using setInterval method,
- ```javascript
- setInterval(function () {
- console.log("Good morning");
- }, 2000);
- ```
+ ```javascript
+ setInterval(function () {
+ console.log("Good morning");
+ }, 2000);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
109. ### Why is JavaScript treated as Single threaded
- JavaScript is a single-threaded language. Because the language specification does not allow the programmer to write code so that the interpreter can run parts of it in parallel in multiple threads or processes. Whereas languages like java, go, C++ can make multi-threaded and multi-process programs.
+ JavaScript is a single-threaded language. Because the language specification does not allow the programmer to write code so that the interpreter can run parts of it in parallel in multiple threads or processes. Whereas languages like java, go, C++ can make multi-threaded and multi-process programs.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
110. ### What is an event delegation
- Event delegation is a technique for listening to events where you delegate a parent element as the listener for all of the events that happen inside it.
+ Event delegation is a technique for listening to events where you delegate a parent element as the listener for all of the events that happen inside it.
- For example, if you wanted to detect field changes inside a specific form, you can use event delegation technique,
+ For example, if you wanted to detect field changes inside a specific form, you can use event delegation technique,
- ```javascript
- var form = document.querySelector("#registration-form");
-
- // Listen for changes to fields inside the form
- form.addEventListener(
- "input",
- function (event) {
- // Log the field that was changed
- console.log(event.target);
- },
- false
- );
- ```
+ ```javascript
+ var form = document.querySelector("#registration-form");
+
+ // Listen for changes to fields inside the form
+ form.addEventListener(
+ "input",
+ function (event) {
+ // Log the field that was changed
+ console.log(event.target);
+ },
+ false
+ );
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
111. ### What is ECMAScript
- ECMAScript is the scripting language that forms the basis of JavaScript. ECMAScript standardized by the ECMA International standards organization in the ECMA-262 and ECMA-402 specifications. The first edition of ECMAScript was released in 1997.
+ ECMAScript is the scripting language that forms the basis of JavaScript. ECMAScript standardized by the ECMA International standards organization in the ECMA-262 and ECMA-402 specifications. The first edition of ECMAScript was released in 1997.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
112. ### What is JSON
- JSON (JavaScript Object Notation) is a lightweight format that is used for data interchanging. It is based on a subset of JavaScript language in the way objects are built in JavaScript.
+ JSON (JavaScript Object Notation) is a lightweight format that is used for data interchanging. It is based on a subset of JavaScript language in the way objects are built in JavaScript.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
113. ### What are the syntax rules of JSON
- Below are the list of syntax rules of JSON
+ Below are the list of syntax rules of JSON
- 1. The data is in name/value pairs
- 2. The data is separated by commas
- 3. Curly braces hold objects
- 4. Square brackets hold arrays
+ 1. The data is in name/value pairs
+ 2. The data is separated by commas
+ 3. Curly braces hold objects
+ 4. Square brackets hold arrays
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
114. ### What is the purpose JSON stringify
- When sending data to a web server, the data has to be in a string format. You can achieve this by converting JSON object into a string using stringify() method.
+ When sending data to a web server, the data has to be in a string format. You can achieve this by converting JSON object into a string using stringify() method.
- ```javascript
- var userJSON = { name: "John", age: 31 };
- var userString = JSON.stringify(userJSON);
- console.log(userString); //"{"name":"John","age":31}"
- ```
+ ```javascript
+ var userJSON = { name: "John", age: 31 };
+ var userString = JSON.stringify(userJSON);
+ console.log(userString); //"{"name":"John","age":31}"
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
115. ### How do you parse JSON string
- When receiving the data from a web server, the data is always in a string format. But you can convert this string value to a javascript object using parse() method.
+ When receiving the data from a web server, the data is always in a string format. But you can convert this string value to a javascript object using parse() method.
- ```javascript
- var userString = '{"name":"John","age":31}';
- var userJSON = JSON.parse(userString);
- console.log(userJSON); // {name: "John", age: 31}
- ```
+ ```javascript
+ var userString = '{"name":"John","age":31}';
+ var userJSON = JSON.parse(userString);
+ console.log(userJSON); // {name: "John", age: 31}
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
116. ### Why do you need JSON
- When exchanging data between a browser and a server, the data can only be text. Since JSON is text only, it can easily be sent to and from a server, and used as a data format by any programming language.
+ When exchanging data between a browser and a server, the data can only be text. Since JSON is text only, it can easily be sent to and from a server, and used as a data format by any programming language.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
117. ### What are PWAs
- Progressive web applications (PWAs) are a type of mobile app delivered through the web, built using common web technologies including HTML, CSS and JavaScript. These PWAs are deployed to servers, accessible through URLs, and indexed by search engines.
+ Progressive web applications (PWAs) are a type of mobile app delivered through the web, built using common web technologies including HTML, CSS and JavaScript. These PWAs are deployed to servers, accessible through URLs, and indexed by search engines.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
118. ### What is the purpose of clearTimeout method
- The clearTimeout() function is used in javascript to clear the timeout which has been set by setTimeout()function before that. i.e, The return value of setTimeout() function is stored in a variable and it’s passed into the clearTimeout() function to clear the timer.
+ The clearTimeout() function is used in javascript to clear the timeout which has been set by setTimeout()function before that. i.e, The return value of setTimeout() function is stored in a variable and it’s passed into the clearTimeout() function to clear the timer.
- For example, the below setTimeout method is used to display the message after 3 seconds. This timeout can be cleared by the clearTimeout() method.
+ For example, the below setTimeout method is used to display the message after 3 seconds. This timeout can be cleared by the clearTimeout() method.
- ```javascript
-
- ```
+ function stop() {
+ clearTimeout(msg);
+ }
+
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
119. ### What is the purpose of clearInterval method
- The clearInterval() function is used in javascript to clear the interval which has been set by setInterval() function. i.e, The return value returned by setInterval() function is stored in a variable and it’s passed into the clearInterval() function to clear the interval.
+ The clearInterval() function is used in javascript to clear the interval which has been set by setInterval() function. i.e, The return value returned by setInterval() function is stored in a variable and it’s passed into the clearInterval() function to clear the interval.
- For example, the below setInterval method is used to display the message for every 3 seconds. This interval can be cleared by the clearInterval() method.
+ For example, the below setInterval method is used to display the message for every 3 seconds. This interval can be cleared by the clearInterval() method.
- ```javascript
-
- ```
+ function stop() {
+ clearInterval(msg);
+ }
+
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
120. ### How do you redirect new page in javascript
- In vanilla javascript, you can redirect to a new page using the `location` property of window object. The syntax would be as follows,
+ In vanilla javascript, you can redirect to a new page using the `location` property of window object. The syntax would be as follows,
- ```javascript
- function redirect() {
- window.location.href = "newPage.html";
- }
- ```
+ ```javascript
+ function redirect() {
+ window.location.href = "newPage.html";
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
121. ### How do you check whether a string contains a substring
- There are 3 possible ways to check whether a string contains a substring or not,
+ There are 3 possible ways to check whether a string contains a substring or not,
- 1. **Using includes:** ES6 provided `String.prototype.includes` method to test a string contains a substring
+ 1. **Using includes:** ES6 provided `String.prototype.includes` method to test a string contains a substring
- ```javascript
- var mainString = "hello",
- subString = "hell";
- mainString.includes(subString);
- ```
+ ```javascript
+ var mainString = "hello",
+ subString = "hell";
+ mainString.includes(subString);
+ ```
- 2. **Using indexOf:** In an ES5 or older environment, you can use `String.prototype.indexOf` which returns the index of a substring. If the index value is not equal to -1 then it means the substring exists in the main string.
+ 2. **Using indexOf:** In an ES5 or older environment, you can use `String.prototype.indexOf` which returns the index of a substring. If the index value is not equal to -1 then it means the substring exists in the main string.
- ```javascript
- var mainString = "hello",
- subString = "hell";
- mainString.indexOf(subString) !== -1;
- ```
+ ```javascript
+ var mainString = "hello",
+ subString = "hell";
+ mainString.indexOf(subString) !== -1;
+ ```
- 3. **Using RegEx:** The advanced solution is using Regular expression's test method(`RegExp.test`), which allows for testing for against regular expressions
+ 3. **Using RegEx:** The advanced solution is using Regular expression's test method(`RegExp.test`), which allows for testing for against regular expressions
- ```javascript
- var mainString = "hello",
- regex = /hell/;
- regex.test(mainString);
- ```
+ ```javascript
+ var mainString = "hello",
+ regex = /hell/;
+ regex.test(mainString);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
122. ### How do you validate an email in javascript
- You can validate an email in javascript using regular expressions. It is recommended to do validations on the server side instead of the client side. Because the javascript can be disabled on the client side.
+ You can validate an email in javascript using regular expressions. It is recommended to do validations on the server side instead of the client side. Because the javascript can be disabled on the client side.
- ```javascript
- function validateEmail(email) {
- var re =
- /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
- return re.test(String(email).toLowerCase());
- }
- ```
+ ```javascript
+ function validateEmail(email) {
+ var re =
+ /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
+ return re.test(String(email).toLowerCase());
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
- The above regular expression accepts unicode characters.
+ The above regular expression accepts unicode characters.
123. ### How do you get the current url with javascript
- You can use `window.location.href` expression to get the current url path and you can use the same expression for updating the URL too. You can also use `document.URL` for read-only purposes but this solution has issues in FF.
+ You can use `window.location.href` expression to get the current url path and you can use the same expression for updating the URL too. You can also use `document.URL` for read-only purposes but this solution has issues in FF.
- ```javascript
- console.log("location.href", window.location.href); // Returns full URL
- ```
+ ```javascript
+ console.log("location.href", window.location.href); // Returns full URL
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
124. ### What are the various url properties of location object
- The below `Location` object properties can be used to access URL components of the page,
+ The below `Location` object properties can be used to access URL components of the page,
- 1. href - The entire URL
- 2. protocol - The protocol of the URL
- 3. host - The hostname and port of the URL
- 4. hostname - The hostname of the URL
- 5. port - The port number in the URL
- 6. pathname - The path name of the URL
- 7. search - The query portion of the URL
- 8. hash - The anchor portion of the URL
+ 1. href - The entire URL
+ 2. protocol - The protocol of the URL
+ 3. host - The hostname and port of the URL
+ 4. hostname - The hostname of the URL
+ 5. port - The port number in the URL
+ 6. pathname - The path name of the URL
+ 7. search - The query portion of the URL
+ 8. hash - The anchor portion of the URL
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
125. ### How do get query string values in javascript
- You can use URLSearchParams to get query string values in javascript. Let's see an example to get the client code value from URL query string,
+ You can use URLSearchParams to get query string values in javascript. Let's see an example to get the client code value from URL query string,
- ```javascript
- const urlParams = new URLSearchParams(window.location.search);
- const clientCode = urlParams.get("clientCode");
- ```
+ ```javascript
+ const urlParams = new URLSearchParams(window.location.search);
+ const clientCode = urlParams.get("clientCode");
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
126. ### How do you check if a key exists in an object
- You can check whether a key exists in an object or not using three approaches,
+ You can check whether a key exists in an object or not using three approaches,
- 1. **Using in operator:** You can use the in operator whether a key exists in an object or not
+ 1. **Using in operator:** You can use the in operator whether a key exists in an object or not
- ```javascript
- "key" in obj;
- ```
+ ```javascript
+ "key" in obj;
+ ```
- and If you want to check if a key doesn't exist, remember to use parenthesis,
+ and If you want to check if a key doesn't exist, remember to use parenthesis,
- ```javascript
- !("key" in obj);
- ```
+ ```javascript
+ !("key" in obj);
+ ```
- 2. **Using hasOwnProperty method:** You can use `hasOwnProperty` to particularly test for properties of the object instance (and not inherited properties)
+ 2. **Using hasOwnProperty method:** You can use `hasOwnProperty` to particularly test for properties of the object instance (and not inherited properties)
- ```javascript
- obj.hasOwnProperty("key"); // true
- ```
+ ```javascript
+ obj.hasOwnProperty("key"); // true
+ ```
- 3. **Using undefined comparison:** If you access a non-existing property from an object, the result is undefined. Let’s compare the properties against undefined to determine the existence of the property.
+ 3. **Using undefined comparison:** If you access a non-existing property from an object, the result is undefined. Let’s compare the properties against undefined to determine the existence of the property.
- ```javascript
- const user = {
- name: "John",
- };
+ ```javascript
+ const user = {
+ name: "John",
+ };
- console.log(user.name !== undefined); // true
- console.log(user.nickName !== undefined); // false
- ```
+ console.log(user.name !== undefined); // true
+ console.log(user.nickName !== undefined); // false
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
127. ### How do you loop through or enumerate javascript object
- You can use the `for-in` loop to loop through javascript object. You can also make sure that the key you get is an actual property of an object, and doesn't come from the prototype using `hasOwnProperty` method.
+ You can use the `for-in` loop to loop through javascript object. You can also make sure that the key you get is an actual property of an object, and doesn't come from the prototype using `hasOwnProperty` method.
- ```javascript
- var object = {
- k1: "value1",
- k2: "value2",
- k3: "value3",
- };
+ ```javascript
+ var object = {
+ k1: "value1",
+ k2: "value2",
+ k3: "value3",
+ };
- for (var key in object) {
- if (object.hasOwnProperty(key)) {
- console.log(key + " -> " + object[key]); // k1 -> value1 ...
- }
- }
- ```
+ for (var key in object) {
+ if (object.hasOwnProperty(key)) {
+ console.log(key + " -> " + object[key]); // k1 -> value1 ...
+ }
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
128. ### How do you test for an empty object
- There are different solutions based on ECMAScript versions
+ There are different solutions based on ECMAScript versions
- 1. **Using Object entries(ECMA 7+):** You can use object entries length along with constructor type.
+ 1. **Using Object entries(ECMA 7+):** You can use object entries length along with constructor type.
- ```javascript
- Object.entries(obj).length === 0 && obj.constructor === Object; // Since date object length is 0, you need to check constructor check as well
- ```
+ ```javascript
+ Object.entries(obj).length === 0 && obj.constructor === Object; // Since date object length is 0, you need to check constructor check as well
+ ```
- 2. **Using Object keys(ECMA 5+):** You can use object keys length along with constructor type.
+ 2. **Using Object keys(ECMA 5+):** You can use object keys length along with constructor type.
- ```javascript
- Object.keys(obj).length === 0 && obj.constructor === Object; // Since date object length is 0, you need to check constructor check as well
- ```
+ ```javascript
+ Object.keys(obj).length === 0 && obj.constructor === Object; // Since date object length is 0, you need to check constructor check as well
+ ```
- 3. **Using for-in with hasOwnProperty(Pre-ECMA 5):** You can use a for-in loop along with hasOwnProperty.
+ 3. **Using for-in with hasOwnProperty(Pre-ECMA 5):** You can use a for-in loop along with hasOwnProperty.
- ```javascript
- function isEmpty(obj) {
- for (var prop in obj) {
- if (obj.hasOwnProperty(prop)) {
- return false;
- }
- }
+ ```javascript
+ function isEmpty(obj) {
+ for (var prop in obj) {
+ if (obj.hasOwnProperty(prop)) {
+ return false;
+ }
+ }
- return JSON.stringify(obj) === JSON.stringify({});
- }
- ```
+ return JSON.stringify(obj) === JSON.stringify({});
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
129. ### What is an arguments object
- The arguments object is an Array-like object accessible inside functions that contains the values of the arguments passed to that function. For example, let's see how to use arguments object inside sum function,
+ The arguments object is an Array-like object accessible inside functions that contains the values of the arguments passed to that function. For example, let's see how to use arguments object inside sum function,
- ```javascript
- function sum() {
- var total = 0;
- for (var i = 0, len = arguments.length; i < len; ++i) {
- total += arguments[i];
- }
- return total;
- }
+ ```javascript
+ function sum() {
+ var total = 0;
+ for (var i = 0, len = arguments.length; i < len; ++i) {
+ total += arguments[i];
+ }
+ return total;
+ }
- sum(1, 2, 3); // returns 6
- ```
+ sum(1, 2, 3); // returns 6
+ ```
- **Note:** You can't apply array methods on arguments object. But you can convert into a regular array as below.
+ **Note:** You can't apply array methods on arguments object. But you can convert into a regular array as below.
- ```javascript
- var argsArray = Array.prototype.slice.call(arguments);
- ```
+ ```javascript
+ var argsArray = Array.prototype.slice.call(arguments);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
130. ### How do you make first letter of the string in an uppercase
- You can create a function which uses a chain of string methods such as charAt, toUpperCase and slice methods to generate a string with the first letter in uppercase.
+ You can create a function which uses a chain of string methods such as charAt, toUpperCase and slice methods to generate a string with the first letter in uppercase.
- ```javascript
- function capitalizeFirstLetter(string) {
- return string.charAt(0).toUpperCase() + string.slice(1);
- }
- ```
+ ```javascript
+ function capitalizeFirstLetter(string) {
+ return string.charAt(0).toUpperCase() + string.slice(1);
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
131. ### What are the pros and cons of for loops
- The for-loop is a commonly used iteration syntax in javascript. It has both pros and cons
+ The for-loop is a commonly used iteration syntax in javascript. It has both pros and cons
- #### Pros
+ #### Pros
- 1. Works on every environment
- 2. You can use break and continue flow control statements
+ 1. Works on every environment
+ 2. You can use break and continue flow control statements
- #### Cons
+ #### Cons
- 3. Too verbose
- 4. Imperative
- 5. You might face off-by-one errors.
+ 3. Too verbose
+ 4. Imperative
+ 5. You might face off-by-one errors.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
132. ### How do you display the current date in javascript
- You can use `new Date()` to generate a new Date object containing the current date and time. For example, let's display the current date in mm/dd/yyyy
+ You can use `new Date()` to generate a new Date object containing the current date and time. For example, let's display the current date in mm/dd/yyyy
- ```javascript
- var today = new Date();
- var dd = String(today.getDate()).padStart(2, "0");
- var mm = String(today.getMonth() + 1).padStart(2, "0"); //January is 0!
- var yyyy = today.getFullYear();
+ ```javascript
+ var today = new Date();
+ var dd = String(today.getDate()).padStart(2, "0");
+ var mm = String(today.getMonth() + 1).padStart(2, "0"); //January is 0!
+ var yyyy = today.getFullYear();
- today = mm + "/" + dd + "/" + yyyy;
- document.write(today);
- ```
+ today = mm + "/" + dd + "/" + yyyy;
+ document.write(today);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
133. ### How do you compare two date objects
- You need to use date.getTime() method in order to compare unix timestamp values
+ You need to use date.getTime() method in order to compare unix timestamp values
- ```javascript
- var d1 = new Date();
- var d2 = new Date(d1);
- console.log(d1.getTime() === d2.getTime()); //True
- console.log(d1 === d2); // False
- ```
+ ```javascript
+ var d1 = new Date();
+ var d2 = new Date(d1);
+ console.log(d1.getTime() === d2.getTime()); //True
+ console.log(d1 === d2); // False
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
134. ### How do you check if a string starts with another string
- You can use ECMAScript 6's `String.prototype.startsWith()` method to check if a string starts with another string or not. But it is not yet supported in all browsers. Let's see an example to see this usage,
+ You can use ECMAScript 6's `String.prototype.startsWith()` method to check if a string starts with another string or not. But it is not yet supported in all browsers. Let's see an example to see this usage,
- ```javascript
- "Good morning".startsWith("Good"); // true
- "Good morning".startsWith("morning"); // false
- ```
+ ```javascript
+ "Good morning".startsWith("Good"); // true
+ "Good morning".startsWith("morning"); // false
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
135. ### How do you trim a string in javascript
- JavaScript provided a trim method on string types to trim any whitespaces present at the beginning or ending of the string.
+ JavaScript provided a trim method on string types to trim any whitespaces present at the beginning or ending of the string.
- ```javascript
- " Hello World ".trim(); //Hello World
- ```
+ ```javascript
+ " Hello World ".trim(); //Hello World
+ ```
- If your browser(";
- }
- ```
+ ```javascript
+ for (i = 0; i < 10; i++) {
+ if (i === 5) {
+ break;
+ }
+ text += "Number: " + i + " ";
+ }
+ ```
- The continue statement is used to "jump over" one iteration in the loop. i.e, It breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.
+ The continue statement is used to "jump over" one iteration in the loop. i.e, It breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.
- ```javascript
- for (i = 0; i < 10; i++) {
- if (i === 5) {
- continue;
- }
- text += "Number: " + i + " ";
- }
- ```
+ ```javascript
+ for (i = 0; i < 10; i++) {
+ if (i === 5) {
+ continue;
+ }
+ text += "Number: " + i + " ";
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
145. ### What are js labels
- The label statement allows us to name loops and blocks in JavaScript. We can then use these labels to refer back to the code later. For example, the below code with labels avoids printing the numbers when they are same,
+ The label statement allows us to name loops and blocks in JavaScript. We can then use these labels to refer back to the code later. For example, the below code with labels avoids printing the numbers when they are same,
- ```javascript
- var i, j;
+ ```javascript
+ var i, j;
- loop1: for (i = 0; i < 3; i++) {
- loop2: for (j = 0; j < 3; j++) {
- if (i === j) {
- continue loop1;
- }
- console.log("i = " + i + ", j = " + j);
- }
- }
+ loop1: for (i = 0; i < 3; i++) {
+ loop2: for (j = 0; j < 3; j++) {
+ if (i === j) {
+ continue loop1;
+ }
+ console.log("i = " + i + ", j = " + j);
+ }
+ }
- // Output is:
- // "i = 1, j = 0"
- // "i = 2, j = 0"
- // "i = 2, j = 1"
- ```
+ // Output is:
+ // "i = 1, j = 0"
+ // "i = 2, j = 0"
+ // "i = 2, j = 1"
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
146. ### What are the benefits of keeping declarations at the top
- It is recommended to keep all declarations at the top of each script or function. The benefits of doing this are,
+ It is recommended to keep all declarations at the top of each script or function. The benefits of doing this are,
- 1. Gives cleaner code
- 2. It provides a single place to look for local variables
- 3. Easy to avoid unwanted global variables
- 4. It reduces the possibility of unwanted re-declarations
+ 1. Gives cleaner code
+ 2. It provides a single place to look for local variables
+ 3. Easy to avoid unwanted global variables
+ 4. It reduces the possibility of unwanted re-declarations
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
147. ### What are the benefits of initializing variables
- It is recommended to initialize variables because of the below benefits,
+ It is recommended to initialize variables because of the below benefits,
- 1. It gives cleaner code
- 2. It provides a single place to initialize variables
- 3. Avoid undefined values in the code
+ 1. It gives cleaner code
+ 2. It provides a single place to initialize variables
+ 3. Avoid undefined values in the code
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
148. ### What are the recommendations to create new object
- It is recommended to avoid creating new objects using `new Object()`. Instead you can initialize values based on it's type to create the objects.
+ It is recommended to avoid creating new objects using `new Object()`. Instead you can initialize values based on it's type to create the objects.
- 1. Assign {} instead of new Object()
- 2. Assign "" instead of new String()
- 3. Assign 0 instead of new Number()
- 4. Assign false instead of new Boolean()
- 5. Assign [] instead of new Array()
- 6. Assign /()/ instead of new RegExp()
- 7. Assign function (){} instead of new Function()
+ 1. Assign {} instead of new Object()
+ 2. Assign "" instead of new String()
+ 3. Assign 0 instead of new Number()
+ 4. Assign false instead of new Boolean()
+ 5. Assign [] instead of new Array()
+ 6. Assign /()/ instead of new RegExp()
+ 7. Assign function (){} instead of new Function()
- You can define them as an example,
+ You can define them as an example,
- ```javascript
- var v1 = {};
- var v2 = "";
- var v3 = 0;
- var v4 = false;
- var v5 = [];
- var v6 = /()/;
- var v7 = function () {};
- ```
+ ```javascript
+ var v1 = {};
+ var v2 = "";
+ var v3 = 0;
+ var v4 = false;
+ var v5 = [];
+ var v6 = /()/;
+ var v7 = function () {};
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
149. ### How do you define JSON arrays
- JSON arrays are written inside square brackets and arrays contain javascript objects. For example, the JSON array of users would be as below,
+ JSON arrays are written inside square brackets and arrays contain javascript objects. For example, the JSON array of users would be as below,
- ```javascript
- "users":[
- {"firstName":"John", "lastName":"Abrahm"},
- {"firstName":"Anna", "lastName":"Smith"},
- {"firstName":"Shane", "lastName":"Warn"}
- ]
- ```
+ ```javascript
+ "users":[
+ {"firstName":"John", "lastName":"Abrahm"},
+ {"firstName":"Anna", "lastName":"Smith"},
+ {"firstName":"Shane", "lastName":"Warn"}
+ ]
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
150. ### How do you generate random integers
- You can use `Math.random()` with `Math.floor()` to return random integers. For example, if you want generate random integers between 1 to 10, the multiplication factor should be 10,
+ You can use `Math.random()` with `Math.floor()` to return random integers. For example, if you want generate random integers between 1 to 10, the multiplication factor should be 10,
- ```javascript
- Math.floor(Math.random() * 10) + 1; // returns a random integer from 1 to 10
- Math.floor(Math.random() * 100) + 1; // returns a random integer from 1 to 100
- ```
+ ```javascript
+ Math.floor(Math.random() * 10) + 1; // returns a random integer from 1 to 10
+ Math.floor(Math.random() * 100) + 1; // returns a random integer from 1 to 100
+ ```
- **Note:** `Math.random()` returns a random number between 0 (inclusive), and 1 (exclusive)
+ **Note:** `Math.random()` returns a random number between 0 (inclusive), and 1 (exclusive)
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
151. ### Can you write a random integers function to print integers within a range
- Yes, you can create a proper random function to return a random number between min and max (both included)
+ Yes, you can create a proper random function to return a random number between min and max (both included)
- ```javascript
- function randomInteger(min, max) {
- return Math.floor(Math.random() * (max - min + 1)) + min;
- }
- randomInteger(1, 100); // returns a random integer from 1 to 100
- randomInteger(1, 1000); // returns a random integer from 1 to 1000
- ```
+ ```javascript
+ function randomInteger(min, max) {
+ return Math.floor(Math.random() * (max - min + 1)) + min;
+ }
+ randomInteger(1, 100); // returns a random integer from 1 to 100
+ randomInteger(1, 1000); // returns a random integer from 1 to 1000
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
152. ### What is tree shaking
- Tree shaking is a form of dead code elimination. It means that unused modules will not be included in the bundle during the build process and for that it relies on the static structure of ES2015 module syntax,( i.e. import and export). Initially this has been popularized by the ES2015 module bundler `rollup`, these days practically all bundlers use this technique.
+ Tree shaking is a form of dead code elimination. It means that unused modules will not be included in the bundle during the build process and for that it relies on the static structure of ES2015 module syntax,( i.e. import and export). Initially this has been popularized by the ES2015 module bundler `rollup`, these days practically all bundlers use this technique.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
153. ### What is the need of tree shaking
- Tree Shaking can significantly reduce the code size in any application. i.e, The less code we send over the wire the more performant the application will be. For example, if we just want to create a “Hello World” Application using SPA frameworks then it will take around a few MBs, but by tree shaking it can bring down the size to just a few hundred KBs. Tree shaking is implemented in Rollup and Webpack bundlers.
+ Tree Shaking can significantly reduce the code size in any application. i.e, The less code we send over the wire the more performant the application will be. For example, if we just want to create a “Hello World” Application using SPA frameworks then it will take around a few MBs, but by tree shaking it can bring down the size to just a few hundred KBs. Tree shaking is implemented in Rollup and Webpack bundlers.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
154. ### Is it recommended to use eval
- No, it allows arbitrary code to be run which causes a security problem. As we know that the eval() function is used to run text as code. In most of the cases, it should not be necessary to use it.
+ No, it allows arbitrary code to be run which causes a security problem. As we know that the eval() function is used to run text as code. In most of the cases, it should not be necessary to use it.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
155. ### What is a Regular Expression
- A regular expression is a sequence of characters that forms a search pattern. You can use this search pattern for searching data in a text. These can be used to perform all types of text search and text replace operations. Let's see the syntax format now,
+ A regular expression is a sequence of characters that forms a search pattern. You can use this search pattern for searching data in a text. These can be used to perform all types of text search and text replace operations. Let's see the syntax format now,
- ```javascript
- /pattern/modifiers;
- ```
+ ```javascript
+ /pattern/modifiers;
+ ```
- For example, the regular expression or search pattern with case-insensitive username would be,
+ For example, the regular expression or search pattern with case-insensitive username would be,
- ```javascript
- /John/i;
- ```
+ ```javascript
+ /John/i;
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
156. ### What are the string methods that accept Regular expression
- There are six string methods: `search()`, `replace()`, `replaceAll()`, `match()`, `matchAll()`, and `split()`.
+ There are six string methods: `search()`, `replace()`, `replaceAll()`, `match()`, `matchAll()`, and `split()`.
- The `search()` method uses an expression to search for a match, and returns the position of the match.
+ The `search()` method uses an expression to search for a match, and returns the position of the match.
- ```javascript
- var msg = "Hello John";
- var n = msg.search(/John/i); // 6
- ```
+ ```javascript
+ var msg = "Hello John";
+ var n = msg.search(/John/i); // 6
+ ```
- The `replace()` and `replaceAll()` methods are used to return a modified string where the pattern is replaced.
+ The `replace()` and `replaceAll()` methods are used to return a modified string where the pattern is replaced.
- ```javascript
- var msg = "ball bat";
- var n1 = msg.replace(/b/i, "c"); // call bat
- var n2 = msg.replaceAll(/b/i, "c"); // call cat
- ```
+ ```javascript
+ var msg = "ball bat";
+ var n1 = msg.replace(/b/i, "c"); // call bat
+ var n2 = msg.replaceAll(/b/i, "c"); // call cat
+ ```
- The `match()` and `matchAll()` methods are used to return the matches when matching a string against a regular expression.
+ The `match()` and `matchAll()` methods are used to return the matches when matching a string against a regular expression.
- ```javascript
- var msg = "Hello John";
- var n1 = msg.match(/[A-Z]/g); // ["H", "J"]
- var n2 = msg.matchAll(/[A-Z]/g); // this returns an iterator
- ```
+ ```javascript
+ var msg = "Hello John";
+ var n1 = msg.match(/[A-Z]/g); // ["H", "J"]
+ var n2 = msg.matchAll(/[A-Z]/g); // this returns an iterator
+ ```
- The `split()` method is used to split a string into an array of substrings, and returns the new array.
+ The `split()` method is used to split a string into an array of substrings, and returns the new array.
- ```javascript
- var msg = "Hello John";
- var n = msg.split(/\s/); // ["Hello", "John"]
- ```
+ ```javascript
+ var msg = "Hello John";
+ var n = msg.split(/\s/); // ["Hello", "John"]
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
157. ### What are modifiers in regular expression
- Modifiers can be used to perform case-insensitive and global searches. Let's list some of the modifiers,
+ Modifiers can be used to perform case-insensitive and global searches. Let's list some of the modifiers,
- | Modifier | Description |
- | -------- | ------------------------------------------------------- |
- | i | Perform case-insensitive matching |
- | g | Perform a global match rather than stops at first match |
- | m | Perform multiline matching |
+ | Modifier | Description |
+ | -------- | ------------------------------------------------------- |
+ | i | Perform case-insensitive matching |
+ | g | Perform a global match rather than stops at first match |
+ | m | Perform multiline matching |
- Let's take an example of global modifier,
+ Let's take an example of global modifier,
- ```javascript
- var text = "Learn JS one by one";
- var pattern = /one/g;
- var result = text.match(pattern); // one,one
- ```
+ ```javascript
+ var text = "Learn JS one by one";
+ var pattern = /one/g;
+ var result = text.match(pattern); // one,one
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
158. ### What are regular expression patterns
- Regular Expressions provide a group of patterns in order to match characters. Basically they are categorized into 3 types,
-
- 1. **Brackets:** These are used to find a range of characters.
- For example, below are some use cases,
- 1. [abc]: Used to find any of the characters between the brackets(a,b,c)
- 2. [0-9]: Used to find any of the digits between the brackets
- 3. (a|b): Used to find any of the alternatives separated with |
- 2. **Metacharacters:** These are characters with a special meaning.
- For example, below are some use cases,
- 1. \\d: Used to find a digit
- 2. \\s: Used to find a whitespace character
- 3. \\b: Used to find a match at the beginning or ending of a word
- 3. **Quantifiers:** These are useful to define quantities.
- For example, below are some use cases,
- 1. n+: Used to find matches for any string that contains at least one n
- 2. n\*: Used to find matches for any string that contains zero or more occurrences of n
- 3. n?: Used to find matches for any string that contains zero or one occurrences of n
+ Regular Expressions provide a group of patterns in order to match characters. Basically they are categorized into 3 types,
+
+ 1. **Brackets:** These are used to find a range of characters.
+ For example, below are some use cases,
+ 1. [abc]: Used to find any of the characters between the brackets(a,b,c)
+ 2. [0-9]: Used to find any of the digits between the brackets
+ 3. (a|b): Used to find any of the alternatives separated with |
+ 2. **Metacharacters:** These are characters with a special meaning.
+ For example, below are some use cases,
+ 1. \\d: Used to find a digit
+ 2. \\s: Used to find a whitespace character
+ 3. \\b: Used to find a match at the beginning or ending of a word
+ 3. **Quantifiers:** These are useful to define quantities.
+ For example, below are some use cases,
+ 1. n+: Used to find matches for any string that contains at least one n
+ 2. n\*: Used to find matches for any string that contains zero or more occurrences of n
+ 3. n?: Used to find matches for any string that contains zero or one occurrences of n
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
159. ### What is a RegExp object
- RegExp object is a regular expression object with predefined properties and methods. Let's see the simple usage of RegExp object,
+ RegExp object is a regular expression object with predefined properties and methods. Let's see the simple usage of RegExp object,
- ```javascript
- var regexp = new RegExp("\\w+");
- console.log(regexp);
- // expected output: /\w+/
- ```
+ ```javascript
+ var regexp = new RegExp("\\w+");
+ console.log(regexp);
+ // expected output: /\w+/
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
160. ### How do you search a string for a pattern
- You can use the `test()` method of regular expression in order to search a string for a pattern, and return true or false depending on the result.
+ You can use the `test()` method of regular expression in order to search a string for a pattern, and return true or false depending on the result.
- ```javascript
- var pattern = /you/;
- console.log(pattern.test("How are you?")); //true
- ```
+ ```javascript
+ var pattern = /you/;
+ console.log(pattern.test("How are you?")); //true
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
161. ### What is the purpose of exec method
- The purpose of exec method is similar to test method but it executes a search for a match in a specified string and returns a result array, or null instead of returning true/false.
+ The purpose of exec method is similar to test method but it executes a search for a match in a specified string and returns a result array, or null instead of returning true/false.
- ```javascript
- var pattern = /you/;
- console.log(pattern.exec("How are you?")); //["you", index: 8, input: "How are you?", groups: undefined]
- ```
+ ```javascript
+ var pattern = /you/;
+ console.log(pattern.exec("How are you?")); //["you", index: 8, input: "How are you?", groups: undefined]
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
162. ### How do you change the style of a HTML element
- You can change inline style or classname of a HTML element using javascript DOM-manipulation
+ You can change inline style or classname of a HTML element using javascript DOM-manipulation
- 1. **Using style property:** You can modify inline style using style property
+ 1. **Using style property:** You can modify inline style using style property
- ```javascript
- document.getElementById("title").style.fontSize = "30px";
- ```
+ ```javascript
+ document.getElementById("title").style.fontSize = "30px";
+ ```
- 2. **Using ClassName property:** It is easy to modify element class using className property
+ 2. **Using ClassName property:** It is easy to modify element class using className property
- ```javascript
- document.getElementById("title").className = "custom-title";
- ```
+ ```javascript
+ document.getElementById("title").className = "custom-title";
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
163. ### What would be the result of 1+2+'3'
- The output is going to be `33`. Since `1` and `2` are numeric values, the result of the first two digits is going to be a numeric value `3`. The next digit is a string type value because of that the addition of numeric value `3` and string type value `3` is just going to be a concatenation value `33`. Other operationrs like `3 * '3'` do yield correct results because the string is coerced into a number.
+ The output is going to be `33`. Since `1` and `2` are numeric values, the result of the first two digits is going to be a numeric value `3`. The next digit is a string type value because of that the addition of numeric value `3` and string type value `3` is just going to be a concatenation value `33`. Other operationrs like `3 * '3'` do yield correct results because the string is coerced into a number.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
164. ### What is a debugger statement
- The debugger statement invokes any available debugging functionality, such as setting a breakpoint. If no debugging functionality is available, this statement has no effect.
- For example, in the below function a debugger statement has been inserted. So
- execution is paused at the debugger statement just like a breakpoint in the script source.
+ The debugger statement invokes any available debugging functionality, such as setting a breakpoint. If no debugging functionality is available, this statement has no effect.
+ For example, in the below function a debugger statement has been inserted. So
+ execution is paused at the debugger statement just like a breakpoint in the script source.
- ```javascript
- function getProfile() {
- // code goes here
- debugger;
- // code goes here
- }
- ```
+ ```javascript
+ function getProfile() {
+ // code goes here
+ debugger;
+ // code goes here
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
165. ### What is the purpose of breakpoints in debugging
- You can set breakpoints in the javascript code once the debugger statement is executed and the debugger window pops up. At each breakpoint, javascript will stop executing, and let you examine the JavaScript values. After examining values, you can resume the execution of code using the play button.
+ You can set breakpoints in the javascript code once the debugger statement is executed and the debugger window pops up. At each breakpoint, javascript will stop executing, and let you examine the JavaScript values. After examining values, you can resume the execution of code using the play button.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
166. ### Can I use reserved words as identifiers
- No, you cannot use the reserved words as variables, labels, object or function names. Let's see one simple example,
+ No, you cannot use the reserved words as variables, labels, object or function names. Let's see one simple example,
- ```javascript
- var else = "hello"; // Uncaught SyntaxError: Unexpected token else
- ```
+ ```javascript
+ var else = "hello"; // Uncaught SyntaxError: Unexpected token else
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
167. ### How do you detect a mobile browser
- You can use regex which returns a true or false value depending on whether or not the user is browsing with a mobile.
+ You can use regex which returns a true or false value depending on whether or not the user is browsing with a mobile.
- ```javascript
- window.mobilecheck = function () {
- var mobileCheck = false;
- (function (a) {
- if (
- /(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i.test(
- a
- ) ||
- /1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test(
- a.substr(0, 4)
- )
- )
- mobileCheck = true;
- })(navigator.userAgent || navigator.vendor || window.opera);
- return mobileCheck;
- };
- ```
+ ```javascript
+ window.mobilecheck = function () {
+ var mobileCheck = false;
+ (function (a) {
+ if (
+ /(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i.test(
+ a
+ ) ||
+ /1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test(
+ a.substr(0, 4)
+ )
+ )
+ mobileCheck = true;
+ })(navigator.userAgent || navigator.vendor || window.opera);
+ return mobileCheck;
+ };
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
168. ### How do you detect a mobile browser without regexp
- You can detect mobile browsers by simply running through a list of devices and checking if the useragent matches anything. This is an alternative solution for RegExp usage,
+ You can detect mobile browsers by simply running through a list of devices and checking if the useragent matches anything. This is an alternative solution for RegExp usage,
- ```javascript
- function detectmob() {
- if (
- navigator.userAgent.match(/Android/i) ||
- navigator.userAgent.match(/webOS/i) ||
- navigator.userAgent.match(/iPhone/i) ||
- navigator.userAgent.match(/iPad/i) ||
- navigator.userAgent.match(/iPod/i) ||
- navigator.userAgent.match(/BlackBerry/i) ||
- navigator.userAgent.match(/Windows Phone/i)
- ) {
- return true;
- } else {
- return false;
- }
- }
- ```
+ ```javascript
+ function detectmob() {
+ if (
+ navigator.userAgent.match(/Android/i) ||
+ navigator.userAgent.match(/webOS/i) ||
+ navigator.userAgent.match(/iPhone/i) ||
+ navigator.userAgent.match(/iPad/i) ||
+ navigator.userAgent.match(/iPod/i) ||
+ navigator.userAgent.match(/BlackBerry/i) ||
+ navigator.userAgent.match(/Windows Phone/i)
+ ) {
+ return true;
+ } else {
+ return false;
+ }
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
169. ### How do you get the image width and height using JS
- You can programmatically get the image and check the dimensions(width and height) using Javascript.
+ You can programmatically get the image and check the dimensions(width and height) using Javascript.
- ```javascript
- var img = new Image();
- img.onload = function () {
- console.log(this.width + "x" + this.height);
- };
- img.src = "http://www.google.com/intl/en_ALL/images/logo.gif";
- ```
+ ```javascript
+ var img = new Image();
+ img.onload = function () {
+ console.log(this.width + "x" + this.height);
+ };
+ img.src = "http://www.google.com/intl/en_ALL/images/logo.gif";
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
170. ### How do you make synchronous HTTP request
- Browsers provide an XMLHttpRequest object which can be used to make synchronous HTTP requests from JavaScript.
+ Browsers provide an XMLHttpRequest object which can be used to make synchronous HTTP requests from JavaScript.
- ```javascript
- function httpGet(theUrl) {
- var xmlHttpReq = new XMLHttpRequest();
- xmlHttpReq.open("GET", theUrl, false); // false for synchronous request
- xmlHttpReq.send(null);
- return xmlHttpReq.responseText;
- }
- ```
+ ```javascript
+ function httpGet(theUrl) {
+ var xmlHttpReq = new XMLHttpRequest();
+ xmlHttpReq.open("GET", theUrl, false); // false for synchronous request
+ xmlHttpReq.send(null);
+ return xmlHttpReq.responseText;
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
171. ### How do you make asynchronous HTTP request
- Browsers provide an XMLHttpRequest object which can be used to make asynchronous HTTP requests from JavaScript by passing the 3rd parameter as true.
+ Browsers provide an XMLHttpRequest object which can be used to make asynchronous HTTP requests from JavaScript by passing the 3rd parameter as true.
- ```javascript
- function httpGetAsync(theUrl, callback) {
- var xmlHttpReq = new XMLHttpRequest();
- xmlHttpReq.onreadystatechange = function () {
- if (xmlHttpReq.readyState == 4 && xmlHttpReq.status == 200)
- callback(xmlHttpReq.responseText);
- };
- xmlHttpReq.open("GET", theUrl, true); // true for asynchronous
- xmlHttpReq.send(null);
- }
- ```
+ ```javascript
+ function httpGetAsync(theUrl, callback) {
+ var xmlHttpReq = new XMLHttpRequest();
+ xmlHttpReq.onreadystatechange = function () {
+ if (xmlHttpReq.readyState == 4 && xmlHttpReq.status == 200)
+ callback(xmlHttpReq.responseText);
+ };
+ xmlHttpReq.open("GET", theUrl, true); // true for asynchronous
+ xmlHttpReq.send(null);
+ }
+ ```
- Today this is considered deprecated, because an async `fetch` call (in browsers later than 2016) is simpler and more robust.
+ Today this is considered deprecated, because an async `fetch` call (in browsers later than 2016) is simpler and more robust.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
172. ### How do you convert date to another timezone in javascript
- You can use the toLocaleString() method to convert dates in one timezone to another. For example, let's convert current date to British English timezone as below,
+ You can use the toLocaleString() method to convert dates in one timezone to another. For example, let's convert current date to British English timezone as below,
- ```javascript
- console.log(new Date().toLocaleString("en-GB", { timeZone: "UTC" })); //29/06/2019, 09:56:00
- ```
+ ```javascript
+ console.log(new Date().toLocaleString("en-GB", { timeZone: "UTC" })); //29/06/2019, 09:56:00
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
173. ### What are the properties used to get size of window
- You can use innerWidth, innerHeight, clientWidth, clientHeight properties of windows, document element and document body objects to find the size of a window. Let's use them combination of these properties to calculate the size of a window or document,
+ You can use innerWidth, innerHeight, clientWidth, clientHeight properties of windows, document element and document body objects to find the size of a window. Let's use them combination of these properties to calculate the size of a window or document,
- ```javascript
- var width =
- window.innerWidth ||
- document.documentElement.clientWidth ||
- document.body.clientWidth;
-
- var height =
- window.innerHeight ||
- document.documentElement.clientHeight ||
- document.body.clientHeight;
- ```
+ ```javascript
+ var width =
+ window.innerWidth ||
+ document.documentElement.clientWidth ||
+ document.body.clientWidth;
+
+ var height =
+ window.innerHeight ||
+ document.documentElement.clientHeight ||
+ document.body.clientHeight;
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
174. ### What is a conditional operator in javascript
- The conditional (ternary) operator is the only JavaScript operator that takes three operands which acts as a shortcut for `if` statements.
+ The conditional (ternary) operator is the only JavaScript operator that takes three operands which acts as a shortcut for `if` statements.
- ```javascript
- var isAuthenticated = false;
- console.log(
- isAuthenticated ? "Hello, welcome" : "Sorry, you are not authenticated"
- ); // Sorry, you are not authenticated
- ```
+ ```javascript
+ var isAuthenticated = false;
+ console.log(
+ isAuthenticated ? "Hello, welcome" : "Sorry, you are not authenticated"
+ ); // Sorry, you are not authenticated
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
175. ### Can you apply chaining on conditional operator
- Yes, you can apply chaining on conditional operators similar to **`if … else if … else if … else`** chain. The syntax is going to be as below,
+ Yes, you can apply chaining on conditional operators similar to **`if … else if … else if … else`** chain. The syntax is going to be as below,
- ```javascript
- function traceValue(someParam) {
- return condition1
- ? value1
- : condition2
- ? value2
- : condition3
- ? value3
- : value4;
- }
+ ```javascript
+ function traceValue(someParam) {
+ return condition1
+ ? value1
+ : condition2
+ ? value2
+ : condition3
+ ? value3
+ : value4;
+ }
- // The above conditional operator is equivalent to:
+ // The above conditional operator is equivalent to:
- function traceValue(someParam) {
- if (condition1) {
- return value1;
- } else if (condition2) {
- return value2;
- } else if (condition3) {
- return value3;
- } else {
- return value4;
- }
- }
- ```
+ function traceValue(someParam) {
+ if (condition1) {
+ return value1;
+ } else if (condition2) {
+ return value2;
+ } else if (condition3) {
+ return value3;
+ } else {
+ return value4;
+ }
+ }
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
176. ### What are the ways to execute javascript after a page load
- You can execute javascript after page load in many different ways,
+ You can execute javascript after page load in many different ways,
- 1. **window.onload:**
+ 1. **window.onload:**
- ```javascript
- window.onload = function ...
- ```
+ ```javascript
+ window.onload = function ...
+ ```
- 2. **document.onload:**
+ 2. **document.onload:**
- ```javascript
- document.onload = function ...
- ```
+ ```javascript
+ document.onload = function ...
+ ```
- 3. **body onload:**
+ 3. **body onload:**
- ```javascript
-
- ```
+ ```javascript
+
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
177. ### What is the difference between proto and prototype
- The `__proto__` object is the actual object that is used in the lookup chain to resolve methods, etc. Whereas `prototype` is the object that is used to build `__proto__` when you create an object with the `new` operator (a special variant of a function call).
+ The `__proto__` object is the actual object that is used in the lookup chain to resolve methods, etc. Whereas `prototype` is the object that is used to build `__proto__` when you create an object with the `new` operator (a special variant of a function call).
- ```javascript
- new Employee().__proto__ === Employee.prototype;
- new Employee().prototype === undefined;
- ```
+ ```javascript
+ new Employee().__proto__ === Employee.prototype;
+ new Employee().prototype === undefined;
+ ```
- There are few more differences,
+ There are few more differences,
- | feature | Prototype | proto |
- | ---------- | ------------------------------------------------------------ | ---------------------------------------------------------- |
- | Access | All function constructors have prototype properties. | All objects have \_\_proto\_\_ property |
- | Purpose | Used to reduce memory wastage with a single copy of function | Used in lookup chain to resolve methods, constructors etc. |
- | ECMAScript | Introduced in ES6 | Introduced in ES5 |
- | Usage | Frequently used | Rarely used |
+ | feature | Prototype | proto |
+ | ---------- | ------------------------------------------------------------ | ---------------------------------------------------------- |
+ | Access | All function constructors have prototype properties. | All objects have \_\_proto\_\_ property |
+ | Purpose | Used to reduce memory wastage with a single copy of function | Used in lookup chain to resolve methods, constructors etc. |
+ | ECMAScript | Introduced in ES6 | Introduced in ES5 |
+ | Usage | Frequently used | Rarely used |
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
178. ### Can you give an example of when you really need a semicolon
- It is recommended to use semicolons after every statement in JavaScript. For example, in the below case (that is an IIFE = Immediately Invoked Function Expression) it throws an error ".. is not a function" at runtime due to missing semicolon.
+ It is recommended to use semicolons after every statement in JavaScript. For example, in the below case (that is an IIFE = Immediately Invoked Function Expression) it throws an error ".. is not a function" at runtime due to missing semicolon.
- ```javascript
- // define a function
- var fn = (function () {
- //...
- })(
- // semicolon missing at this line
-
- // then execute some code inside a closure
- function () {
- //...
- }
- )();
- ```
+ ```javascript
+ // define a function
+ var fn = (function () {
+ //...
+ })(
+ // semicolon missing at this line
+
+ // then execute some code inside a closure
+ function () {
+ //...
+ }
+ )();
+ ```
- and it will be interpreted as
+ and it will be interpreted as
- ```javascript
- var fn = (function () {
- //...
- })(function () {
- //...
- })();
- ```
+ ```javascript
+ var fn = (function () {
+ //...
+ })(function () {
+ //...
+ })();
+ ```
- In this case, we are passing the second function as an argument to the first function and then trying to call the result of the first function call as a function. Hence, the second function will fail with a "... is not a function" error at runtime.
+ In this case, we are passing the second function as an argument to the first function and then trying to call the result of the first function call as a function. Hence, the second function will fail with a "... is not a function" error at runtime.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
179. ### What is the freeze method
- The **`freeze()`** method is used to freeze an object. Freezing an object does not allow adding new properties to an object, prevents removing, and prevents changing the enumerability, configurability, or writability of existing properties. i.e. It returns the passed object and does not create a frozen copy.
+ The **`freeze()`** method is used to freeze an object. Freezing an object does not allow adding new properties to an object, prevents removing, and prevents changing the enumerability, configurability, or writability of existing properties. i.e. It returns the passed object and does not create a frozen copy.
- ```javascript
- const obj = {
- prop: 100,
- };
+ ```javascript
+ const obj = {
+ prop: 100,
+ };
- Object.freeze(obj);
- obj.prop = 200; // Throws an error in strict mode
+ Object.freeze(obj);
+ obj.prop = 200; // Throws an error in strict mode
- console.log(obj.prop); //100
- ```
+ console.log(obj.prop); //100
+ ```
- Remember freezing is only applied to the top-level properties in objects but not for nested objects.
- For example, let's try to freeze user object which has employment details as nested object and observe that details have been changed.
+ Remember freezing is only applied to the top-level properties in objects but not for nested objects.
+ For example, let's try to freeze user object which has employment details as nested object and observe that details have been changed.
- ```javascript
- const user = {
- name: "John",
- employment: {
- department: "IT",
- },
- };
+ ```javascript
+ const user = {
+ name: "John",
+ employment: {
+ department: "IT",
+ },
+ };
- Object.freeze(user);
- user.employment.department = "HR";
- ```
+ Object.freeze(user);
+ user.employment.department = "HR";
+ ```
- **Note:** It causes a TypeError if the argument passed is not an object.
+ **Note:** It causes a TypeError if the argument passed is not an object.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
180. ### What is the purpose of the freeze method
- Below are the main benefits of using freeze method,
+ Below are the main benefits of using freeze method,
- 1. It is used for freezing objects and arrays.
- 2. It is used to make an object immutable.
+ 1. It is used for freezing objects and arrays.
+ 2. It is used to make an object immutable.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
181. ### Why do I need to use the freeze method
- In the Object-oriented paradigm, an existing API contains certain elements that are not intended to be extended, modified, or re-used outside of their current context. Hence it works as the `final` keyword which is used in various languages.
+ In the Object-oriented paradigm, an existing API contains certain elements that are not intended to be extended, modified, or re-used outside of their current context. Hence it works as the `final` keyword which is used in various languages.
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
182. ### How do you detect a browser language preference
- You can use the navigator object to detect a browser language preference as below,
+ You can use the navigator object to detect a browser language preference as below,
- ```javascript
- var language =
- (navigator.languages && navigator.languages[0]) || // Chrome / Firefox
- navigator.language || // All browsers
- navigator.userLanguage; // IE <= 10
+ ```javascript
+ var language =
+ (navigator.languages && navigator.languages[0]) || // Chrome / Firefox
+ navigator.language || // All browsers
+ navigator.userLanguage; // IE <= 10
- console.log(language);
- ```
+ console.log(language);
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
183. ### How to convert a string to title case with javascript
- Title case means that the first letter of each word is capitalized. You can convert a string to title case using the below function,
+ Title case means that the first letter of each word is capitalized. You can convert a string to title case using the below function,
- ```javascript
- function toTitleCase(str) {
- return str.replace(/\w\S*/g, function (txt) {
- return txt.charAt(0).toUpperCase() + txt.substring(1).toLowerCase();
- });
- }
- toTitleCase("good morning john"); // Good Morning John
- ```
+ ```javascript
+ function toTitleCase(str) {
+ return str.replace(/\w\S*/g, function (txt) {
+ return txt.charAt(0).toUpperCase() + txt.substring(1).toLowerCase();
+ });
+ }
+ toTitleCase("good morning john"); // Good Morning John
+ ```
- **[⬆ Back to Top](#table-of-contents)**
+ **[⬆ Back to Top](#table-of-contents)**
184. ### How do you detect if javascript is disabled on the page
- You can use the `