Edit: in 2019-april-2
in express@4.16.0 the body-parser middleware is included in express, so you don’t need to install body-parser separately anymore. for more details see this
OLD:
To handle HTTP POST requests in Express.js version 4 and above, you need to install the middleware module called body-parser.
body-parser extracts the entire body portion of an incoming request stream and exposes it on req.body.
The middleware was a part of Express.js earlier but now you have to install it separately.
This body-parser module parses the JSON, buffer, string and URL encoded data submitted using HTTP POST request. Install body-parser using NPM as shown below.
npm install body-parser --save