Express.js res.json() Function

The res.json() function sends a JSON response. This method sends a response (with the correct content-type) that is the parameter converted to a JSON string using the JSON.stringify() method.

Syntax:

res.json( [body] )

Parameters: The body parameter is the body that is to be sent in the response.

Return Value: It returns an Object.

Installation of the express module:

You can visit the link to Install the express module. You can install this package by using this command. 

npm install express

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

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

Project Structure:

Example 1: Filename: index.js

javascript

const express = require('express');
const app = express();
const PORT = 3000;

// Without middleware
app.get('/', function (req, res) {
    res.json({ user: 'geek' });
});

app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Steps to run the program:

Make sure you have installed the express module using the following command: 

npm install express

Run the index.js file using the below command: 

node index.js

Output:

Console Output:

Server listening on PORT 3000

Browser Output:

Now open the browser and go to http://localhost:3000/, now on your screen you will see the following output: 

{"user":"geek"}

Example 2: Filename: index.js

javascript

const express = require('express');
const app = express();
const PORT = 3000;

// With middleware
app.use('/', function (req, res, next) {
    res.json({ title: "GeeksforGeeks" })
    next();
})

app.get('/', function (req, res) {
    console.log("User Page")
    res.end();
});

app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Steps to run the program:

Run the index.js file using the below command: 

node index.js

Output:

Browser Output:

Now open a browser and go to http://localhost:3000/, now on your screen you will see the following output: 

{"title":"GeeksforGeeks"}

Console Output:

And you will see the following output on your console: 

User Page

Reference: https://expressjs.com/en/4x/api.html#res.json