Intro

Get going with Express JS

ExpressJS is a web server for NodeJS.

Port numbers

When starting a ExpressJS server it binds a process to a port number on the server it’s started on. Port numbers allow one to start multiple ExpressJS server instances on the same server, each one with it’s own port number.

This example starts a server instance on port 3000:

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

//start the server
var server = app.listen(3000);

This server instance is not useful, as it expose no routes.

Routes

Routes can be accessed using the HTTP protocol. ExpressJS support all the HTTP request verbs. We will focus on POST and GET requests.

To add a hello route to the server add the code below before the app.listen method call.

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

Our server instance now has a /hello HTTP GET route.

Setup and run a ExpressJS server instance

Follow these steps to setup a ExpressJS server instance

• Create a new folder in your projects folder called express-app.
• Change into this folder using cd express-app.
• Type npm init. This will create a package.json file in the current directory, based on your answers to some questions.
  • entry point means the main file for your application. We’re going to use server.js, so enter that.
  • test command for us is mocha. We’ll use this feature of the package.json later, for automatic testing of our code.
  • git repository is the location of your repository, like https://github.com/<username>/<repository>.git. Since we’re using GitHub to store our code, npm lets us use a shortcut like this: <username>/<repository>.
• Install ExpressJS and save it as a dependency in your package.json by running npm install --save express. The additional --save parameter makes npm add a line to your package.json file.

Read more details about installing ExpressJS here.

Basic Express server instance

Now create a file called server.js and copy the code below into it:

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

// create a route
app.get('/', function (req, res) {
 res.send('Hello World!');
});

//start the server
var server = app.listen(3000, function () {

 var host = server.address().address;
 var port = server.address().port;

 console.log('Example app listening at http://%s:%s', host, port);

});

Now try this:

• Start the server by typing node server.js and press enter in the console.
• In a web browser navigate to http://localhost:3000/
• Stop the server in the console by pressing Ctrl-C in the console a few times.
• Now navigate to http://localhost:3000/ again. What happens?
• Start the server and again.
• Try to navigate to http://localhost:3000/hello - what happens? How can we fix that?
• Try this:
  • Stop the web server.
  • Add a new route for /hello that renders ‘Hello codeX!’ to the screen.
  • Start the server.
  • Now try to navigate to http://localhost:3000/hello What happened?