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index.html
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<html>
<head>
<link rel="stylesheet" href="codemirror.css">
<script src="codemirror.js"></script>
<script src="javascript.js"></script>
<style type="text/css">
.all {width: 750px; }
textarea, pre { -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; }
.output { background-color: #CCCCCC; border: 1px black solid; overflow:scroll }
.code { font-family:monospace }
.model { font-family:monospace;width:500px;height:400px }
.illegal { color:red }
.legal {color: green }
.question { border: solid 1px black;}
.lesson {visibility:hidden; }
.post { visibility:hidden}
.aside { font-size:smaller }
.verifier { display:none }
.answer { display:none }
</style>
<style type="text/css">.CodeMirror {border: 1px solid black;}</style>
<script type="text/javascript" src="rx.js"></script>
<script type="text/javascript" src="rx.time.js"></script>
<script src="jquery.min.js"></script>
<script src="knockout-2.2.0rc.js"></script>
<script>
var seq = function(array, interval) {
interval = interval || 500;
return Rx.Observable.create(function(observer) {
var counter = 0,
lastValue,
timeoutSubscription = null,
unsubscribed = false;
function doWork() {
if (counter === array.length) {
if (lastValue !== undefined) {
observer.onCompleted();
return;
}
}
lastValue = array[counter];
if (lastValue === undefined) {
counter++;
timeoutSubscription = window.setTimeout(doWork, interval);
}
else {
counter++;
observer.onNext(lastValue);
if (!unsubscribed) {
doWork();
}
}
}
doWork();
return function() {
unsubscribed = true;
if (timeoutSubscription !== null) {
testing = window.clearTimeout(timeoutSubscription);
}
};
});
};
var jQueryMock = {
getJSON: function(url, bag) {
if (Math.random() > 0.9) {
if (bag.error) {
bag.error("There was a connectivity error.");
}
}
else if (url.indexOf("abTestInformation") !== -1) {
window.setTimeout(
function() {
bag.success({ urlPrefix: "billboardTest" });
},
500);
}
else if (url.indexOf("config") !== -1) {
window.setTimeout(
function() {
bag.success({ showInstantQueue: true });
},
500);
}
else if (url.indexOf("movieLists") !== -1) {
window.setTimeout(
function() {
bag.success({
list: [
{ name: "Thrillers", videos: [234324,234322314,23,5,435,12,3,234,34,23324] },
{ name: "New Releases", videos: [234324,234322314,23,5,435,12,3,234,34,23324] }
]
});
},
500);
}
else if (url.indexOf("queue") !== -1) {
window.setTimeout(
function() {
bag.success({
list: { name: "Instant Queue", videos: [234324,234322314,23,5,435,12,3,234,34,23324] }
});
},
500);
}
}
};
var Observable = Rx.Observable;
Observable.fromEvent = function(dom, eventName, action) {
return Observable.create(function(observer) {
var handler = function(ev) {
if (action !== undefined) {
action(ev);
}
else {
if (ev && ev.preventDefault) {
ev.preventDefault();
}
}
observer.onNext(ev);
};
dom.addEventListener(eventName, handler, false);
return function() {
dom.removeEventListener(eventName, handler, false);
};
});
};
var oldMerge = Observable.prototype.merge;
Observable.prototype.merge = function() {
var args = Array.prototype.slice.call(arguments);
if (arguments.length === 0) {
return Observable.prototype.mergeObservable.apply(this, args);
}
else {
return oldMerge.apply(this, args);
}
}
function deepStringify(obj) {
return JSON.stringify(deepStringifyRecurse(obj));
}
function deepStringifyRecurse(obj) {
var ancestors = [obj],
ancestor,
output = {},
prop,
counter,
value;
if (obj === null || obj === undefined || typeof obj !== "object") {
return obj;
}
ancestor = Object.getPrototypeOf(obj);
while(ancestor !== undefined) {
if (ancestors[ancestors.length-1] === ancestor) {
break;
}
ancestors.push(ancestor);
ancestor = Object.getPrototypeOf(obj);
}
for(counter = ancestors.length-1; counter >= 0; counter--) {
ancestor = ancestors[counter];
for(prop in ancestor) {
output[prop] = deepStringifyRecurse(ancestor[prop]);
}
}
return output;
}
Array.prototype.merge = function() {
var results = [];
this.forEach(function(subArray) {
subArray.forEach(function(itemInArray) {
results.push(itemInArray);
});
});
return results;
};
Array.prototype.mapMany = function(projection) {
return this.
map(function(item) {
return projection(item);
}).
merge();
}
Array.prototype.sortBy = function (keySelector) {
return this.slice().sort(function(a,b) {
var aKey = keySelector(a),
bKey = keySelector(b);
if (aKey > bKey) {
return 1;
}
else if (bKey > aKey) {
return -1;
}
else {
return 0;
}
});
};
Array.prototype.reduce = function(combiner, initialValue) {
var counter,
accumulatedValue;
// If the array is empty, do nothing
if (this.length === 0) {
return this;
}
else {
// If the user didn't pass an initial value, use the first item.
if (arguments.length === 1) {
counter = 1;
accumulatedValue = this[0];
}
else if (arguments.length >= 2) {
counter = 0;
accumulatedValue = initialValue;
}
else {
throw "Invalid arguments.";
}
// Loop through the array, feeding the current value and the result of
// the previous computation back into the combiner function until
// we've exhausted the entire array and are left with only one function.
while(counter < this.length) {
accumulatedValue = combiner(accumulatedValue, this[counter])
counter++;
}
return [accumulatedValue];
}
};
// JSON.stringify(Array.zip([1,2,3],[4,5,6], function(left, right) { return left + right })) === '[5,7,9]' accumulatedValue + currentValue; }); === [6];
Array.zip = function(left, right, combinerFunction) {
var counter,
results = [];
for(counter = 0; counter < Math.min(left.length, right.length); counter++) {
results.push(combinerFunction(left[counter], right[counter]));
}
return results;
};
Rx.Observable.prototype.mapMany = Rx.Observable.prototype.selectMany;
Rx.Observable.prototype.map = Rx.Observable.prototype.select;
Rx.Observable.prototype.filter = Rx.Observable.prototype.where;
Rx.Observable.prototype.forEach = function(onNext, onError, onCompleted) {
return this.subscribe(onNext,onError,onCompleted);
};
Rx.Observable.zip = function(left, right, func) {
return left.zip(right, func);
}
var codeMirrors = [];
var last = new Date();
</script>
<script>
(function($) {
function pasteIntoInput(el, text) {
el.focus();
if (typeof el.selectionStart == "number") {
var val = el.value;
var selStart = el.selectionStart;
el.value = val.slice(0, selStart) + text + val.slice(el.selectionEnd);
el.selectionEnd = el.selectionStart = selStart + text.length;
} else if (typeof document.selection != "undefined") {
var textRange = document.selection.createRange();
textRange.text = text;
textRange.collapse(false);
textRange.select();
}
}
function allowTabChar(el) {
$(el).keydown(function(e) {
if (e.which == 9) {
pasteIntoInput(this, "\t");
return false;
}
});
// For Opera, which only allows suppression of keypress events, not keydown
$(el).keypress(function(e) {
if (e.which == 9) {
return false;
}
});
}
$.fn.allowTabChar = function() {
if (this.jquery) {
this.each(function() {
if (this.nodeType == 1) {
var nodeName = this.nodeName.toLowerCase();
if (nodeName == "textarea" || (nodeName == "input" && this.type == "text")) {
allowTabChar(this);
}
}
})
}
return this;
}
})(jQuery);
function cancelTab(e) {
if (e.which === 9) {
e.preventDefault();
}
}
window.onload = function() {
function save() {
var answers = [];
$(".lesson").each(function(cnt,item) {
var go = $(".go", item)[0],
code = $(".code", item)[0];
if (window.getComputedStyle(item).visibility !== "hidden") {
answers.push($(code).val());
}
});
localStorage.setItem("newState", JSON.stringify({answers: answers}));
}
// This code adds a reduce question in the middle
var state = localStorage.getItem("state");
if (state) {
state = JSON.parse(state);
state.answers.splice(18,0,$("#q18").val());
localStorage.setItem("newState", JSON.stringify(state));
delete localStorage.state;
}
var state = localStorage.getItem("newState");
if (state) {
state = JSON.parse(state);
var firstUnfinishedQuestion;
$(".lesson").each(function(cnt,item) {
var go = $(".go", item)[0],
code = $(".code", item)[0],
post = $(".post", item)[0];
if (cnt < state.answers.length) {
$(code).val(state.answers[cnt]);
item.style.visibility = "visible";
if (post !== undefined) {
post.style.visibility = "visible";
}
}
else if (cnt === state.answers.length) {
item.style.visibility = "visible";
}
});
}
//$(function() {
//$("textarea").allowTabChar();
//});
$(function() {
var lessons = $(".lesson");
lessons.each(function(cnt,item) {
var go = $(".go", item)[0],
code = $(".code", item)[0],
output = $(".output", item)[0],
showAnswer= $(".showAnswer", item)[0],
answer= $(".answer", item)[0],
codeMirror = CodeMirror.fromTextArea(code, {
lineNumbers: true,
matchBrackets: true,
mode: "text/typescript",
tabSize: 4,
indentWithTabs: true
}),
post = $(".post", item)[0],
verifierScript = $(".verifier", item)[0],
controls = $(".control", item);
codeMirrors.push(codeMirror);
go.onclick = function() {
try {
var verifier = eval("(" + verifierScript.innerText + ")");
try {
codeMirror.save();
save();
verifier($(code).val(), item);
if (post !== undefined) {
post.style.visibility = "visible";
}
if (cnt < lessons.length-1) {
lessons[cnt+1].style.visibility = "visible";
}
}
catch(ex) {
alert(ex);
}
}
catch(ex) {
alert(ex);
}
};
if (showAnswer) {
showAnswer.onclick = function() {
codeMirror.setValue(answer.innerText);
};
}
});
});
}
</script>
</head>
<body style="font-family:sans-serif">
<div class="all">
<h1>Functional Programming in Javascript: Hands on Lab</h1>
<a href="javascript:delete localStorage.newState; document.location.reload();">Restart Lab</a>
<h2>Traversing an Array</h2>
<div class="lesson" style="visibility:visible">
<h3>Exercise 1: Print all the names in an array</h3>
<textarea class="code" rows="8" cols="80">
function(console) {
var names = ["Ben", "Jafar", "Matt", "Priya", "Brian"],
counter;
for(var counter = 0; counter < names.length; counter++) {
console.log(names[counter]);
}
}
</textarea><button class="go">Run</button><span class="aside"><- Click here to try your solution. If it works, you'll move on to the next exercise.</span>
<div class="output">
</div>
<pre class="verifier">
// Traverse array with for loop
function(str) {
var fun = eval("(" + str + ")");
var items =[];
fun({
log:function(name) {
items.push(name);
console.log(name);
}
});
if(JSON.stringify(items.sort()) === '["Ben","Brian","Jafar","Matt","Priya"]') {
return "Success!"
}
else {
throw 'console.log did not receive all of these values: "Ben","Brian","Jafar","Matt","Priya" (note: order does not matter)'
}
}
</pre>
<pre class="answer">
function(console) {
var names = ["Ben", "Jafar", "Matt", "Priya", "Brian"],
counter;
for(var counter = 0; counter < names.length; counter++) {
console.log(names[counter]);
}
}
</pre>
<p class="post">Ask yourself this question: <b>did we need to specify the <i>order</i> in which the names were printed?</b> If not, why do it?</p>
</div>
<div class="lesson">
<h3>Exercise 2: Use forEach to print all the names in an array</h3>
<p>Let's repeat the previous exercise using the forEach function.</p>
<textarea class="code" rows="8" cols="80">
function(console) {
var names = ["Ben", "Jafar", "Matt", "Priya", "Brian"];
names.forEach(function(name) {
console.log(name);
});
}
</textarea><button class="go">Run</button>
<div class="output">
</div>
<pre class="verifier">
// Traverse array with foreach
function(str) {
if (str.indexOf(".forEach") === -1) {
return "You have to use forEach!"
}
var fun = eval("(" + str + ")");
var items =[];
fun({
log:function(name) {
items.push(name);
console.log(name);
}
});
if(JSON.stringify(items.sort()) === '["Ben","Brian","Jafar","Matt","Priya"]') {
return "Success!"
}
else {
throw 'console.log did not receive all of these values: "Ben","Brian","Jafar","Matt","Priya" (note: order does not matter)'
}
}
</pre>
<pre class="answer">
function(console) {
var names = ["Ben", "Jafar", "Matt", "Priya", "Brian"];
names.forEach(function(name) {
console.log(name);
});
}
</pre>
<p class="post">Notice that forEach let's us specify <i>what</i> we want to happen to each item in the array, but hides <i>how</i> the array is traversed.</p>
</div>
<h2>Projecting Arrays</h2>
<p>Applying a function to a value and creating a new value is called a <i>projection</i>. To project one array into another, we apply a projection function to each item in the array and collect the results in a new array.</p>
<div class="lesson">
<h3>Exercise 3: Project an array of videos into an array of {id,title} pairs using forEach()</h3>
<p>For each video, add a projected {id, title} pair to the videoAndTitlePairs array.</p>
<textarea class="code" rows="60" cols="80">
function() {
var newReleases = [
{
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 654356453,
"title": "Bad Boys",
"boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
},
{
"id": 65432445,
"title": "The Chamber",
"boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 675465,
"title": "Fracture",
"boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
}
],
videoAndTitlePairs = [];
// ------------ INSERT CODE HERE! -----------------------------------
// Use forEach function to accumulate {id, title} pairs from each video.
// Put the results into the videoAndTitlePairs array
// ------------ INSERT CODE HERE! -----------------------------------
return videoAndTitlePairs;
}
</textarea><button class="go">Run</button><button class="showAnswer">Show Answer</button>
<div class="output">
</div>
<pre class="verifier">
// Projection with with forEach
function(str) {
var fun = eval("(" + str + ")"),
videoAndTitlePairs = fun(),
expected = '[{\"id\":675465,\"title\":\"Fracture\"},{\"id\":65432445,\"title\":\"The Chamber\"},{\"id\":70111470,\"title\":\"Die Hard\"},{\"id\":654356453,\"title\":\"Bad Boys\"}]';
// Sorting by video id
videoAndTitlePairs = videoAndTitlePairs.sortBy(function(video) { return video.id });
if (JSON.stringify(videoAndTitlePairs) === expected) {
return true;
}
else {
throw 'Expected: ' + expected;
}
}
</pre>
<pre class="answer">
function() {
var newReleases = [
{
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 654356453,
"title": "Bad Boys",
"boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
},
{
"id": 65432445,
"title": "The Chamber",
"boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 675465,
"title": "Fracture",
"boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
}
],
videoAndTitlePairs = [];
newReleases.forEach(function(video) {
videoAndTitlePairs.push({id:video.id, title: video.title});
});
return videoAndTitlePairs;
}
</pre>
<div class="post">
<p>All array projections share two operations in common:</p>
<ol>
<li>Traverse the source array</li>
<li>Add each item's projected value to a new array</li>
</ol>
<p>Why not abstract away <i>how</i> these operations are carried out?</p>
</div>
</div>
<div class="lesson">
<h3>Exercise 4: Implement map()</h3>
<p>To make projections easier, let's add a <b>map()</b> function to the Array type. Map accepts the projection function to be applied to each item in the source array, and returns the projected array.</p>
<textarea class="code" rows="20" cols="80">
Array.prototype.map = function(projectionFunction) {
var results = [];
this.forEach(function(itemInArray) {
// ------------ INSERT CODE HERE! ----------------------------
// Apply the projectionFunction to each item in the array and add
// each result to the results array.
// Note: you can add items to an array with the push() method.
// ------------ INSERT CODE HERE! ----------------------------
});
return results;
};
// JSON.stringify([1,2,3].map(function(x) { return x + 1; })) === '[2,3,4]'
</textarea><button class="go">Run</button><button class="showAnswer">Show Answer</button>
<div class="output">
</div>
<pre class="verifier">
// Implement map()
function(str) {
var fun = eval(str),
arr = [1,2,3],
result;
result = arr.map(function(x) { return x + 1});
if (JSON.stringify(arr) !== "[1,2,3]") {
throw "Whoa! You changed the input array. Map never changes the value of the array passed in. It creates a new array with the results of applying the projection function to every value in the old array."
}
else if(JSON.stringify(result) !== '[2,3,4]') {
throw 'Expected that [1,2,3].map(function(x) { return x + 1}) would equal [2,3,4].'
}
}
</pre>
<pre class="answer">
Array.prototype.map = function(projectionFunction) {
var results = [];
this.forEach(function(itemInArray) {
results.push(projectionFunction(itemInArray));
});
return results;
};
// JSON.stringify([1,2,3].map(function(x) { return x + 1; })) === '[2,3,4]'
</pre>
</div>
<div class="lesson">
<h3>Exercise 5: Use map() to project an array of videos into an array of {id,title} pairs</h3>
<p>Let's repeat the exercise of collecting {id, title} pairs for each video in the newReleases array, but <b>this time we'll use our map function.</b></p>
<textarea class="code" rows="60" cols="80">
function() {
var newReleases = [
{
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 654356453,
"title": "Bad Boys",
"boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
},
{
"id": 65432445,
"title": "The Chamber",
"boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 675465,
"title": "Fracture",
"boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
}
];
// ------------ INSERT CODE HERE! -----------------------------------
// Use map function to accumulate {id, title} pairs from each video.
return newReleases.map // finish this expression!
// ------------ INSERT CODE HERE! -----------------------------------
}
</textarea><button class="go">Run</button><button class="showAnswer">Show Answer</button>
<div class="output">
</div>
<pre class="verifier">
// Projection with map
function(str) {
var fun = eval("(" + str + ")"),
videoAndTitlePairs = fun(),
expected = '[{\"id\":675465,\"title\":\"Fracture\"},{\"id\":65432445,\"title\":\"The Chamber\"},{\"id\":70111470,\"title\":\"Die Hard\"},{\"id\":654356453,\"title\":\"Bad Boys\"}]';
// Sorting by video id
videoAndTitlePairs = videoAndTitlePairs.sortBy(function(video) { return video.id });
if (JSON.stringify(videoAndTitlePairs) === expected) {
return true;
}
else {
throw 'Expected: ' + expected;
}
}
</pre>
<pre class="answer">
function() {
var newReleases = [
{
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 654356453,
"title": "Bad Boys",
"boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
},
{
"id": 65432445,
"title": "The Chamber",
"boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [4.0],
"bookmark": []
},
{
"id": 675465,
"title": "Fracture",
"boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": [5.0],
"bookmark": [{ id:432534, time:65876586 }]
}
];
return newReleases.map(function(video) { return {id: video.id, title: video.title}; });
}
</pre>
<p class="post">Notice that map allows us to specify <i>what</i> projection we want to apply to an array, but hides <i>how</i> the operation is carried out.</p>
</div>
<h2>Filtering Arrays</h2>
<p>Like projection, filtering an array is also a very common operation. To filter an array we apply a test to each item in the array and collect the items that pass into a new array.</p>
<div class="lesson">
<h3>Exercise 6: Use forEach() to collect only those videos with a rating of 5.0</h3>
<p>Use forEach() to loop through the videos in the newReleases array and, if a video has a rating of 5.0, add it to the videos array.</p>
<textarea class="code" rows="60" cols="80">
function() {
var newReleases = [
{
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 4.0,
"bookmark": []
},
{
"id": 654356453,
"title": "Bad Boys",
"boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 5.0,
"bookmark": [{ id:432534, time:65876586 }]
},
{
"id": 65432445,
"title": "The Chamber",
"boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 4.0,
"bookmark": []
},
{
"id": 675465,
"title": "Fracture",
"boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 5.0,
"bookmark": [{ id:432534, time:65876586 }]
}
],
videos = [];
// ------------ INSERT CODE HERE! -----------------------------------
// Use forEach function to accumulate ever video with a rating of 5.0
// ------------ INSERT CODE HERE! -----------------------------------
return videos;
}
</textarea><button class="go">Run</button><button class="showAnswer">Show Answer</button>
<div class="output">
</div>
<pre class="verifier">
// Filter with forEach
function(str) {
var fun = eval("(" + str + ")"),
videos = fun(),
expected = '[{"id":675465,"title":"Fracture","boxart":"http://cdn-0.nflximg.com/images/2891/Fracture.jpg","uri":"http://api.netflix.com/catalog/titles/movies/70111470","rating":5,"bookmark":[{"id":432534,"time":65876586}]},{"id":654356453,"title":"Bad Boys","boxart":"http://cdn-0.nflximg.com/images/2891/BadBoys.jpg","uri":"http://api.netflix.com/catalog/titles/movies/70111470","rating":5,"bookmark":[{"id":432534,"time":65876586}]}]';
// Sorting by video id
videos = videos.sortBy(function(v) { return v.id; });
if (JSON.stringify(videos) === expected) {
return true;
}
else {
throw 'Expected: ' + expected;
}
}
</pre>
<pre class="answer">
function() {
var newReleases = [
{
"id": 70111470,
"title": "Die Hard",
"boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 4.0,
"bookmark": []
},
{
"id": 654356453,
"title": "Bad Boys",
"boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 5.0,
"bookmark": [{ id:432534, time:65876586 }]
},
{
"id": 65432445,
"title": "The Chamber",
"boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 4.0,
"bookmark": []
},
{
"id": 675465,
"title": "Fracture",
"boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
"uri": "http://api.netflix.com/catalog/titles/movies/70111470",
"rating": 5.0,
"bookmark": [{ id:432534, time:65876586 }]
}
],
videos = [];
newReleases.forEach(function(video) {
if (video.rating === 5.0) {
videos.push(video);
}
});
return videos;
}
</pre>
<div class="post">
<p>Notice that, like map(), <b>every filter() operation shares some operations in common</b>:</p>
<ol>
<li>Traverse the array</li>
<li>Add objects that pass the test to a new array</li>
</ol>
<p>Why not abstract away how these operations are carried out?</p>
</div>
</div>
<div class="lesson">
<h3>Exercise 7: Implement filter()</h3>
<p>To make filtering easier, let's add a filter() function to the Array type. The filter() function accepts a <i>predicate</i>. A predicate is a function that accepts an item in the array, and returns a boolean indicating whether the item should be retained in the new array.</p>
<textarea class="code" rows="20" cols="80">
Array.prototype.filter = function(predicateFunction) {
var results = [];
this.forEach(function(itemInArray) {
// ------------ INSERT CODE HERE! ----------------------------
// Apply the predicateFunction to each item in the array. If the
// result is truthy, add each result to the results array.
// Note: remember you can add items to the array using the array's
// push() method.
// ------------ INSERT CODE HERE! ----------------------------
});
return results;
};
// JSON.stringify([1,2,3].filter(function(x) { return x > 2})) === "[3]"
</textarea><button class="go">Run</button><button class="showAnswer">Show Answer</button>
<div class="output">
</div>
<pre class="verifier">
// Implement filter()
function(str) {
var fun = eval(str),
arr = [1,2,3],
result;
result = arr.filter(function(x) { return x > 2});
if (JSON.stringify(arr) !== "[1,2,3]") {
throw "Whoa! You changed the input array. Filter never changes the value of the array passed in. It creates a new array that includes only those items in the old array that pass the predicate function."
}
else if(JSON.stringify(result) !== '[3]') {
throw 'Expected that [1,2,3].filter(function(x) { return x > 2}) would equal [3].'
}
}
</pre>
<pre class="answer">
Array.prototype.filter = function(predicateFunction) {
var results = [];
this.forEach(function(itemInArray) {
if (predicateFunction(itemInArray)) {