router.use() Method in Express.js

The router.use() method has an optional mount path which is set to "/" by default. This method uses the specified middleware functions for this optional mountpath. The method is similar to app.use().

Syntax

router.use( [path], [function, ...] callback )

Example 1

Create a file with the name "routerUse.js" and copy the following code snippet. After creating the file, use the command "node routerUse.js" to run this code as shown in the example below:

// router.use() Method Demo Example

// Importing the express module
const express = require('express');

// Initializing the express and port number
var app = express();

// Initializing the router from express
var router = express.Router();
var PORT = 3000;

// If the endpoint not found default is called
router.use(function (req, res, next) {
   console.log("Middleware Called");
   next();
})

// This method is always invoked
router.use(function (req, res, next) {
   console.log("Welcome to Tutorials Point");
   res.send("Welcome to Tutorials Point");
})
app.use('/api', router);
app.listen(PORT, function(err){
   if (err) console.log(err);
   console.log("Server listening on PORT", PORT);
});

Hit the following Endpoint with a GET request − http://localhost:3000/api

Output

C:\home
ode>> node routerUse.js
Server listening on PORT 3000
Middleware Called
Welcome to Tutorials Point

Example 2

Let's take a look at one more example.

// router.use() Method Demo Example

// Importing the express module
const express = require('express');

// Initializing the express and port number
var app = express();

// Initializing the router from express
var router = express.Router();
var PORT = 3000;

// All requests will hit this middleware
router.use(function (req, res, next) {
   console.log('Method: %s URL: %s Path: %s', req.method, req.url, req.path)
   next()
})

// this will only be invoked if the path starts with /v1 from the mount point
router.use('/v1', function (req, res, next) {
   console.log("/v1 is called")
   next()
})
// always invoked
router.use(function (req, res, next) {
   res.send('Welcome to Tutorials Point')
})
app.use('/api', router)
app.listen(PORT, function(err){
   if (err) console.log(err);
   console.log("Server listening on PORT", PORT);
});

Hit the following Endpoint one by one with a GET request −

• http://localhost:3000/api
• http://localhost:3000/api/v1

Output

C:\home
ode>> node routerUse.js
Server listening on PORT 3000
Method: GET URL: / Path: /
Method: GET URL: /v1 Path: /v1
/v1 is called