Group requests into a single request

For clients not supporting HTTP/2, but the slower HTTP/1.1, request grouping is one of the 'best practises' to improve performance.
This is a demonstration on how to group requests, if you support HTTP/1.1 as a fallback.

More info:
Looking for a way to unpack the batch requests? This is the example:

POST body containing requests:

Click button to launch function.

JS code:
Click button to show code.