I don't know why you're being downvoted, calling full access javascript embedded into a page a 'tracking pixel' is a total lie. Then again 'serverless' is where you use a server, so the track record isn't great.
I guess most people reading this already knew that the term 'tracking pixel' has evolved beyond its original meaning, and is now commonly understood to include all sorts of tracking code.
I did not, but now I know :)
(And although serverless doesn't mean 'no server', we know what the word means and it doesn't cause confusion.)