What is Express.js？

1. What is Express.js?

Express.js is a free and open-source web application framework for Node.js and is used for designing and building web applications that are running on web browsers and organizing your back-end architecture. Express.js supports JavaScript which is a commonly used programming language. Without Express.js, you have to write your own code to build a routing component which is a time-consuming and tedious task. Express.js offers simplicity, flexibility, efficiency, minimalism, and scalability to programmers. It also has the advantage of powerful performance as it is a framework of Node.js.

2. Install and use Express.js

It can be installed via the Node Package Manager with the command “npm install express”. The basic use would be as below:

// use require function to import express module
const express = require('express');
// create an object
const app = express();
// create a callback function which is called when you access to "http://localhost:3000"
//"app" is an instance of the express module
app.get('/',function(req,res)
{
res.send('Hello World!');
});
const server=app.listen(3000,function() {});

3. Create a routing with Express.js

A routing defines the way in which your application responds to a client request to a particular endpoint. For instance, with Express.js a user can make a GET, POST, PUT or DELETE http request for various URLs such as

http://localhost:3000/admin
http://localhost:3000/student

Each route can have one or more handler functions which are executed whtn the routing path is matched. The syntax would be

app.METHOD(PATH, HANDLER)
/* app : an instance of the express module 
   METHOD : an HTTP request method (GET, POST, PUT, or DELETE)
   PATH : a path on a server
   HANLDER : a function to be executed when the route matches*/

4. Why Express.js?

Here are some of the use cases of Express.js:

1. Using cookies on a website

2. Implementing authentication

3. Adding a search bar to a site

4. Serving static files like images

Also there are several advantages to use Express.js:

1. Allows development of Node.js web application simple and quick.
2. Simple and easy to set up and customization.
3. It lets you identify your application routes based on HTTP methods and URLs.
4. It contains several middleware components that can be used on request and response to conduct extra duties.
5. Easily integrates with various template engines such as Jade, Vash, EJS, etc.
6. It helps you to identify a middleware handling error.
7. Easily handle the application’s static files and services.
8. It enables you to build a server with the REST API.
9. Fast to link to databases like MongoDB, Redis, MySQL.