Express.js express.json() Function - GeeksforGeeks

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 expressAfter installing the express module, you can check your express version in command prompt using the command.npm version expressAfter 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
You can visit the link to Install express module. You can install this package by using this command.npm install express
npm install express
After installing the express module, you can check your express version in command prompt using the command.npm version express
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
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 expressRun index.js file using below command:node index.jsOutput: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

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

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

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
Express.js
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