How to detect when one or more JS/CSS library fail to load (e.g. CDN)?

Question

Premise: I\'ve found these two answers but I don\'t understand how I can sistematically apply it for many libraries:

Detect and log when external Ja

Answer 1

Just add an onerror handler to the tag. This can call a fallback, give the user a message etc.

Example

Using a non-existing url will here pop up an alert:

For custom function, just define a script block in the header before the link tags so you can call a custom function: