Express.js | router.use() Function

The router.use() function uses the specified middleware function or functions. It basically mounts middleware for the routes which are being served by the specific router. Syntax:

router.use( path, function )

Parameters:

1. Path: It is the path to this middleware, like if we can have /user, now this middleware is called for all API’s having /user of this router.
2. function: This function is passed as a callback, it is called when the specified path is called in this router.

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

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

npm version express

1. 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

Filename: index.js

javascript

var express = require('express');
var app = express();
var router = express.Router();
var PORT = 3000;

// All requests to this router will
// first hit this middleware
router.use(function (req, res, next) {
  console.log("Middleware Called");
  next();
})

// Always invoked
router.use(function (req, res, next) {
  res.send("Greetings from GeeksforGeeks");
})

app.use('/user', 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

1. Run index.js file using below command:

node index.js

1. Output:

Server listening on PORT 3000

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

Server listening on PORT 3000
Middleware Called

1. And you will see the following output on your browser:

Greetings from GeeksforGeeks

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