Express.js | router.use() Function

17 Jun, 2020
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:
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.function: This function is passed an a callback, it is called when the specified path is called in this router.
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.
function: This function is passed an a callback, it is called when the specified path is called in this router.
Installation of express module:
You can visit the link to Install express module. You can install this package by using this command.npm install expressAfter installing the express module, you can check your express version in command prompt using the command.npm version expressAfter 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
You can visit the link to Install express module. You can install this package by using this command.npm install express
npm install express
After installing the express module, you can check your express version in command prompt using the command.npm version express
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
node index.js
Filename: index.js
var express = require('express');var app = express();var router = express.Router();var PORT = 3000;  // All requests to this router will// first hit this middlewarerouter.use(function (req, res, next) {  console.log("Middleware Called");  next();})  // Always invokedrouter.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:
The project structure will look like this:Make sure you have installed express module using the following command:npm install expressRun index.js file using below command:node index.jsOutput:Server listening on PORT 3000
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
And you will see the following output on your browser:Greetings from GeeksforGeeks
The project structure will look like this:
Make sure you have installed express module using the following command:npm install express
npm install express
Run index.js file using below command:node index.jsOutput:Server listening on PORT 3000

node index.js
Output:
Server listening on PORT 3000

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
And you will see the following output on your browser:Greetings from GeeksforGeeks
Server listening on PORT 3000
Middleware Called

And you will see the following output on your browser:
Greetings from GeeksforGeeks
Express.js
Node.js
Web Technologies
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
How to update Node.js and NPM to next version ?
Installation of Node.js on Linux
Node.js fs.readFileSync() Method
How to install the previous version of node.js and npm ?
Node.js fs.writeFile() Method
Installation of Node.js on Linux
Top 10 Projects For Beginners To Practice HTML and CSS Skills
Difference between var, let and const keywords in JavaScript
How to insert spaces/tabs in text using HTML/CSS?
How to fetch data from an API in ReactJS ?