Express.js | res.format() Function

The res.format() function performs content-negotiation on the Accept HTTP header on the request object if it is present. This function checks the Accept HTTP request header and then invokes the corresponding handler depending upon the Accept value.



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
  2. After installing the express module, you can check your express version in command prompt using the command.
    npm version express
  3. 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





var express = require('express');
var app = express();
var PORT = 3000;
app.get('/', function(req, res){
        html: function () {
          res.send('<p>Greetings from GeeksforGeeks</p>');
        text: function () {
          res.send('Greetings from GeeksforGeeks');
        json: function () {
          res.send({ message: 'Greetings from GeeksforGeeks' });
app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);


In the above example, the output will be { “message”: “Greetings from GeeksforGeeks” } when the Accept header field is set to ‘application/json’ and if the Accept header field is set to ‘text/plain’, we will get “Greetings from GeeksforGeeks” message in response.

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
  3. Run index.js file using below command:
    node index.js


    Server listening on PORT 3000
  4. Open your browser and go to http://localhost:3000/, now you can see the following output on your screen.
    Greetings from GeeksforGeeks
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