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Express app.use() Function

Last Updated : 08 Jan, 2024
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The app.use() function is used to mount the specified middleware function(s) at the path that is being specified. It is mostly used to set up middleware for your application. 

Syntax:

app.use(path, callback)

Parameters:

  • path: It is the path for which the middleware function is being called. It can be a string representing a path or path pattern or a regular expression pattern to match the paths.
  • callback: It is a middleware function or a series/array of middleware functions.

Steps to create the application:

Step 1: You can install this package by using this command.

npm install express

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

npm version express

Project Structure:

NodeProj

The updated dependencies in package.json file will look like:

"dependencies": {
"express": "^4.18.2",

Example: Below is the code example of middleware.

Javascript




const express = require('express');
const app = express();
const PORT = 3000;
 
// This middleware will not allow the
// request to go beyond it
app.use(function (req, res, next) {
    console.log("Middleware called")
    next();
});
 
// Requests will never reach this route
app.get('/user', function (req, res) {
    console.log("/user request called");
    res.send('Welcome to GeeksforGeeks');
});
 
app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log(`Server listening on PORT ${PORT}`);
});


Steps to run the program:

node index.js

Console Output:

terminalop

Output

Browser Output: Now open your browser and go to http://localhost:3000/user and you can see

browergeeksop

Output

We have a complete list of Express Application module methods, properties and events, to check those please go through this Express.js Application Complete Reference article.


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