Express.js vs KoaJS in Node.js

14 Sep, 2020
Node.js: Node.js is an open-source and cross-platform runtime environment for executing JavaScript code outside a browser. You need to remember that NodeJS is not a framework and it’s not a programming language. Most of the people are confused and understand it’s a framework or a programming language. We often use Node.js for building back-end services like APIs like Web App or Mobile App.
Express Module: In order to use the express module, we need to install the NPM (Node Package Manager) and the following modules (on cmd).
// Creates package.json file
>> npm init 

// Installs express module
>> npm install express --save // OR
>> npm i express -s  

Import express module: Import express module and store returned instance into a variable.
Syntax:
var express = require("express");

Creating Server: The above syntax calls the “express()” function and creates a new express application which gets stored inside the app variable.
Syntax:
// Importing and creating express application
const app = express();  
var express = require("express")(); // OR

Sending and listening to the response: It communicates the request and response with the client and the server. It requires PORT <number> and IP <number> to communicate.  
app.listen(PORT, IP, Callback);

Parameter: This method accepts three parameters as mentioned above and described below:
PORT <Number>: Ports are the endpoints of communication which helps to communicate with the client and the server.
PORT <Number>: Ports are the endpoints of communication which helps to communicate with the client and the server.
IP <Number>: IPs represent IPv4 or IPv6 address of a host or a device.
IP <Number>: IPs represent IPv4 or IPv6 address of a host or a device.
Callback <Function>: It accepts a function.
Callback <Function>: It accepts a function.
The below example illustrates the Express.js module in Node.js.
Example 1: Filename: index.js
// Node.js program to create server  // with help of Express module  // Importing express  const express = require('express');  // Creating new express app  const app = express();  // PORT configurationconst PORT = process.env.PORT || 2020;  // IP configurationconst IP = process.env.IP || 2021;  // Create a route for the appapp.get('/', (req, res) => { res.send('Hello Vikas_g from geeksforgeeks!');});  // Create a route for the appapp.get('*', (req, res) => { res.send('OOPS!! The link is broken...');});  // Server listening to requestsapp.listen(PORT, IP, () => { console.log(`The Server is running     at: http://localhost:${PORT}/`);});
Run index.js file using the following command:
node index.js

Output:
The Server is running at: http://localhost:2020
Now type http://127.0.0.1:2020/ OR http://localhost:2020/ in a web browser to see the output.
KoaJS Module: In order to use the KoaJS module, we need to install the NPM (Node Package Manager) and the following modules (on cmd).
// Creates package.json file
>> npm init

// Installs koa module<
>> npm install koa --save 
>> npm i koa -s  // OR

Import KoaJS module: Import KoaJS module and store returned instance into a variable.
Syntax:
var koa = require("koa"); // Importing koa module

Creating Server: The above syntax imports the koa module and creates a new koa application which gets stored inside the app variable.
Syntax:
const app = new koa();  // Creating koa application

Sending and listening to the response: It communicates the request and response with the client and the server. It requires PORT <number> and IP <number> to communicate.
app.listen(PORT, IP, Callback);

Parameter: This method accepts three parameters as mentioned above and described below:
PORT <Number>: Ports are the endpoints of communication which helps to communicate with the client and the server.
PORT <Number>: Ports are the endpoints of communication which helps to communicate with the client and the server.
IP <Number>: IPs represent IPv4 or IPv6 address of a host or a device.
IP <Number>: IPs represent IPv4 or IPv6 address of a host or a device.
Callback <Function>: It accepts a function.
Callback <Function>: It accepts a function.
The below example illustrates the KoaJS module in Node.js.
Example 2: Filename: index.js
// Node.js program to create server// with help of Koa module  // Importing koa moduleconst koa = require('koa');  // Creating new koa appconst app = new koa();  // PORT configurationconst PORT = process.env.PORT || 2020;  // IP configurationconst IP = process.env.IP || 2021;  app.use(function *() {this.body = "Hello GeeksForGeeks!";});  // Server listening to requestsapp.listen(PORT, IP, ()=>{console.log("Server started at port", PORT);});
Run index.js file using the following command:
node index.js

Output:
The Server is running at port 2020
Now type http://127.0.0.1:2020/ OR http://localhost:2020/ in a web browser to see the output.
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