expressjs

Express Sample Codes

Basics:

• Express is a Node.js web application framework.

• Express is used to make:

1. Websites
2. Web apps
3. Back Ends

• Pug(earlier known as jade) is used to creating HTML templates.

• Competetors: Rails, Django

• Developed by TJ Holowaychuk, maintained by Node.js foundation.

• npm is the package manager for node.

• Packages can be installed using npm install command. The installation can be of two types, either local or global. In local installation the packages will be available only with in the directory. While packages in global can be acessed throughout the system.

  npm install -g name_of_package is the systax for global installation.

  For local installation omit the -g flag.

• npm init is used for creating package.json file. This file is used to list down the dependencies. So it is good if you generate this file.

• Simple Hello world application

  var express = require('express'); var app = express();

  app.get('/', function(req, res){ res.send("Hello world!"); });

  app.listen(3000);

  app.get(route, callback). the get can be replaced by any of the HTTP requests. The callback function will be called when the client requests that url.

  The callback function has two parameters, request(req) & response(res).

• The HTTP requests are also called HTTP verbs at places.

• route is an endpoint in the url. eg. www.example.com/hello here /hello is a route.

• You can have multiple callback methods at the same route. e.g you can have app.get("/", ...), app.put("/", ...), app.get("/", ...), etc.

• You can also use the all method to handle all HTTP requests using a single method. This is benifitial in defining middle wares.

The syntax is:

app.all('/hello', function(req, res){
res.send("This method will handle all the requests.");
});

*Routers: Using routers will make the code more maintainable as the routes are defined in separate file.

• Routes can be either static or dynamic.

• Passing parameters in the url will be an example of Dynamic route. Dynamic routes can be used at any level you want. For eg. at root level or at a sub level, say at /hello.

• You can match patterns in your route, and the requests that escape the pattern can be matched using the * wild card in the route. As express processes the main js file i.e. either app.js or index.js from start to end. Put the match every thing pattern at the end

Examples

Express Hello-World Example: myapp

• Use the npm init command to add package.json file.
• Install express using npm install express.

Express Generator Hello-World Example: genapp

Install the express-generator package using: npm install express-generator -g

But this will install express-generator globally as you have selected the global install options -g.

Genreate the app with pug as the view engine. If you want to change the view engine and see other options: express -h express --view=pug genapp

npm start To start the application.

Open the page localhost:3000

Routing

Routing simply means what action will be taken when there is a client request on a particular URL & a specific HTTP request method.

The key points are:

1. URL

2. HTTP Request Method (GET, POST, PUT, DELETE, HEAD, OPTIONS)

You can use Postman to send HTTP requests you want.