Node.js uses streams to handle incoming data.
Quoting from the docs,
A stream is an abstract interface for working with streaming data in Node.js. The stream module provides a base API that makes it easy to build objects that implement the stream interface.
To handle in request body of a POST request, use the request object, which is a readable stream. Data streams are emitted as data events on the request object.
request.on('data', chunk => {
buffer += chunk;
});
request.on('end', () => {
// POST request body is now available as `buffer`
});
Simply create an empty buffer string and append the buffer data as it received via data events.
NOTE
data events is of type Bufferbuffer string inside the request handler.