[rhapsodic]

>Since early in my career when hiring I've found developers who only know 'jQuery / Angular / Vue / React' but not the underlying Javascript

It's frightening, the degree to which many professional web app developers do not know the fundamentals of Javascript. Our technical interview starts out with ridiculously simple questions and gets progressively more difficult and esoteric. And a dismayingly high number of candidates don't get past the first couple of questions. And these are people with years of experience and at least some of the hot JS frameworks on their resume.