Understanding Requests Body
When receiving a POST or PUT request, the request body might be important to your application. Getting at the body data is a little more involved than accessing request headers. The request object that's passed in to a handler implements the ReadableStream interface. This stream can be listened to or piped elsewhere just like any other stream. We can grab the data right out of the stream by listening to the stream's 'data' and 'end' events.
The chunk emitted in each 'data' event is a Buffer. If you know it's going to be string data, the best thing to do is collect the data in an array, then at the 'end', concatenate and stringify it.
let body = []; request.on('data', (chunk) => { body.push(chunk); }).on('end', () => { body = Buffer.concat(body).toString(); // at this point, `body` has the entire request body stored in it as a string });
Understanding body-parser
As per its documentation
Parse incoming request bodies in a middleware before your handlers, available under the req.body property.
As you saw in the first example, we had to parse the incoming request stream manually to extract the body. This becomes a tad tedious when there are multiple form data of different types. So we use the body-parser package which does all this task under the hood.
It provides four modules to parse different types of data
After having the raw content body-parser will use one of the above strategies(depending on middleware you decided to use) to parse the data. You can read more about them by reading their documentation.
After setting the req.body to the parsed body, body-parser will invoke next() to call the next middleware down the stack, which can then access the request data without having to think about how to unzip and parse it.