Do I need to know JS for parsing?

Question

Parsing

Hello! The question is to broaden one's horizons. When parsing sites (in PHP, Python, Ruby, etc), which have a lot of JS and AJAX, headless browsers, Selenium, etc. are used. Is it necessary to study JS itself in order to better understand what is happening inside, or is it enough to consider this toolkit as a "black box"?

Answer 1

It is necessary, and even more so if headless browsers are used, and not HTTP.
Well, tell me: how do you solve a standard problem, the page is loaded, then AJAX is performed, and only after that the required element appears in the DOM, so it means a standard type event OnDocumentComplete, etc. is useless here, because when it "lights up", then the element will not be there yet?
Although, knowledge of the DOM itself is already knowledge of JS.