Express js First App

We hope, you have successfully installed express. Now let's create a simple first express.js application.

var express = require("Express");
var app = express();

app.get("/", function(request, response){
	response.send("Hello World!");
});

app.listen(3000, function(){ 
	console.log('Server is running at http://localhost:3000');
});

Explanation of the above code

var express = require("Express");

It includes express and puts in a variable.

var app = express();

It creates a new express application inside app variable.

app.get("/", function(request, response){
	response.send("Hello World!");
});

It is a request handler that defines the route and sends 'Hello World'. A request handler is a function that will be executed every time the server receives a particular request, usually defined by HTTP method. It accepts two parameters request and response.

app.listen(3000, function(){ 
	console.log('Server is running at http://localhost:3000');
});

It starts the server on 3000 port.

Run the application

In your working directory, create a file name 'firstapp.js' and save the above code. Now, open command prompt and run the app from the project folder using the following command.

$node firstapp.js

Now open your web browser at 'http://localhost:3000'.

How Express.js works

Express.js has a main file, that is the main entry file. This file may contain configuration settings, template engine, routes, define middleware such as static file handler, error handling, cookies and other parsers.