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 the express module:

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

npm install express

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

npm version express

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

Project Structure:

Example 1: Filename: index.js

javascript

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

// Single routing
const 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:

Make sure you have installed the express module using the following command:

npm install express

Run the index.js file using the below command:

node index.js

Output:

Console Output:

Server listening on PORT 3000

Browser Output:

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

javascript

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

// Multiple routing
const router1 = express.Router();
const router2 = express.Router();
const 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();
});

router3.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);
});

Steps to run the  program:

Run the index.js file using the 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:

Output:

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

Reference: https://expressjs.com/en/4x/api.html#express.router