Where is the .JS file in this code? And why are they calling it this way?

Question

Where is the JS file and is this Async the fastest way to call JS?

I guess they then have PHP calls in the .JS for updating the Ad stats??

The code:

Answer 1

It inserts the script tag with a dynamically constructed file name and puts it in the document before the first script tag. The advantage of this approach is that it will run only when the document is loaded, so it will not block the document loading. This way, the user will experience no (or less) delay. It's a good practise to do this for analytical tools and such, because they don't add functionality for the user and you just want to track their actions. It doesn't matter if you miss one or two of those measurements.