Express.js express.Router() Function

The express.Router() function is used to create a new router object. This function is used when you want to create a new router object in your program to handle requests.

Syntax:

express.Router( [options] )

Optional Parameters:

• case-sensitive: This enables case sensitivity.
• mergeParams: It preserves the req.params values from the parent router.
• strict: This enables strict routing.

Return Value: This function returns the New Router Object.

Installation of express module:

1. You can visit the link to Install express module. You can install this package by using this command.

   npm install express

2. After installing the express module, you can check your express version in command prompt using the command.

   npm version express

3. After that, you can just create a folder and add a file for example, index.js. To run this file you need to run the following command.

   node index.js

Example 1: Filename: index.js

var express = require('express');
var app = express();
var PORT = 3000;

// Single routing
var router = express.Router();

router.get('/', function (req, res, next) {
    console.log("Router Working");
    res.end();
})

app.use(router);

app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Steps to run the program:

1. The project structure will look like this:
   
2. Make sure you have installed express module using the following command:

   npm install express

3. Run index.js file using below command:

   node index.js

   Output:

   Server listening on PORT 3000
   

4. Now open your browser and go to http://localhost:3000/, you will see the following output on your screen:

   Server listening on PORT 3000
   Router Working
   

Example 2: Filename: index.js

var express = require('express');
var app = express();
var PORT = 3000;

// Multiple routing
var router1 = express.Router();
var router2 = express.Router();
var router3 = express.Router();

router1.get('/user', function (req, res, next) {
    console.log("User Router Working");
    res.end();
});

router2.get('/admin', function (req, res, next) {
    console.log("Admin Router Working");
    res.end();
});

router2.get('/student', function (req, res, next) {
    console.log("Student Router Working");
    res.end();
});

app.use(router1);
app.use(router2);
app.use(router3);

app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Run index.js file using below command:

node index.js

Now make a GET request to http://localhost:3000/user, http://localhost:3000/admin and http://localhost:3000/student, then you will see the following output on your console:

Server listening on PORT 3000
User Router Working
Admin Router Working
Student Router Working

Reference: Offical Documentation