Express JS express.json() Function

The express.json() function is a built-in middleware function in Express. It parses incoming requests with JSON payloads and is based on body-parser. 

Syntax:

express.json( [options] )

Parameters: The options parameter has various properties like inflate, limit, type, etc. 

Return Value: It returns an Object. 

Steps to Installation the express module:

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

Step 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

Project Structure:

Project Structure

Example 1: Below is the code example of the express.json().

javascript

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

app.use(express.json());

app.post('/', function (req, res) {
    console.log(req.body.name)
    res.end();
})

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

Steps to run the program:

Step 1:Make sure you have installed the express module using the following command:

npm install express

Step 2: Run the index.js file using the below command:

node index.js

Output: Now make a POST request to http://localhost:3000/ with header set to ‘content-type: application/json’ and body {“name”:”GeeksforGeeks”}, then you will see the following output on your console:

Server listening on PORT 3000
GeeksforGeeks

Example 2: Below is the code example of the express.json().

javascript

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

// Without this middleware
// app.use(express.json());
app.post('/', function (req, res) {
    console.log(req.body.name)
    res.end();
})

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

Steps to run the program:

Step 2: Run the index.js file using the below command:

node index.js

Output: Now make a POST request to http://localhost:3000/ with header set to ‘content-type: application/json’ and body {“name”:”GeeksforGeeks”}, then you will see the following output on your console:

Server listening on PORT 3000
TypeError: Cannot read property 'name' of undefined