I've been a developer since 1988. I used JS a few times for minor touchups but I only used it as a foreground language for about four months.

I didn't like it at all.

The use of var or let for all declarations is simply unacceptable. The language allows all kinds of mistakes; misspell an object field and you have a new field, not a compiler error.

It is a mess of dialects and versions, code that works in one file doesn't compile in another. Why?

And there seems to be no cohesive "idiom"; like a language designed by a committee of aggressively competitive people. I learned enough to get my work done but if I never used it again that would be fine with me.