BB>>А работа с памятью? Где гарантия, что сборка мусора не произойдёт в критический момент?
C>Я не припомню, чтобы сборка мусора в браузере как-то влияла на отзывчивость.

Прямо у самого гугла есть целая страница по куче проблем, которые могут возникнуть с JS https://developers.google.com/web/tools/chrome-devtools/memory-problems

Про GC в самом конце:

If your page appears to pause frequently, then you may have garbage collection issues.

You can use either the Chrome Task Manager or Timeline memory recordings to spot frequent garbage collections. In the Task Manager, frequently rising and falling Memory or JavaScript Memory values represent frequent garbage collections. In Timeline recordings, frequently rising and falling JS heap or node count graphs indicate frequent garbage collections.

Once you've identified the problem, you can use an Allocation Timeline recording to find out where memory is being allocated and which functions are causing the allocations.