Atlas 4: Only 2 calls at a time and don't expect any order
Browsers make 2 concurrent AJAX calls at a time to a domain. If
you make 5 AJAX calls, browser is going to make 2 calls first, then
wait for any one of them to complete and then make another call
until all remaining 4 calls are complete. Moreover, you cannot
expect calls to execute in the same order as you make the calls.
Here's why:
Here you see, call 3's response download is quite big and thus
takes longer than Call 5. So, Call 5 actually gets executed before
Call 3.
So, the world of HTTP is unpredictable.