why is body parser used code example

Example 1: body-parser npm

$ npm install body-parser

Example 2: body-parser doc

var express = require('express')
var bodyParser = require('body-parser')

var app = express()

// create application/json parser
var jsonParser = bodyParser.json()

// create application/x-www-form-urlencoded parser
var urlencodedParser = bodyParser.urlencoded({ extended: false })

// POST /login gets urlencoded bodies
app.post('/login', urlencodedParser, function (req, res) {
  res.send('welcome, ' + req.body.username)
})

// POST /api/users gets JSON bodies
app.post('/api/users', jsonParser, function (req, res) {
  // create user in req.body
})