Express.js express.json() Function

Difficulty Level : Basic
Last Updated : 07 Jul, 2020

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 have various property like inflate, limit, type, etc.

Return Value: It returns an Object.

Installation of express module:

You can visit the link to Install 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 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
```

Example 1: Filename: index.js

var express = require('express');
var app = express();
var 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:

The project structure will look like this:
Make sure you have installed express module using the following command:
```
npm install express
```
Run index.js file using below command:
```
node index.js
```
Output:
```
Server listening on PORT 3000
```
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: Filename: index.js

var express = require('express');
var app = express();
var 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);
});

Run index.js file using below command:

node index.js

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

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

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Express.js express.json() Function