This has nothing to do with undefined vs. exceptions, sorry. You can do example the same with a powerful enough sandbox -- e.g. what WebAsm does to avoid hostil

This has nothing to do with undefined vs. exceptions, sorry. You can do example the same with a powerful enough sandbox -- e.g. what WebAsm does to avoid hostile code taking over your computer. It has everything to do with sandboxing (or not). Ads being served by third parties should not be able to influence the JS running in the page.