Quite the contrary, learning a language
because it is exploding in popularity is a nice way to ensure that you'll end up being abused, poorly paid and irrelevant. You can't possibly find a worse reason for learning a new language.
On Javascript you're missing the causality. Some people are learning Javascript because it is popular of course, because they've read on some forum that learning popular things gets them hired, but those people are totally uninteresting in the pool of developers that learned Javascript because they had shit to do and things to build and Javascript was the answer.
There's a big difference between learning X because you want to make your job easier, because you want to build things in a new way, because you want exposure to new ways of thinking, because there isn't an alternative to what you're trying to do, etc... and learning X because that's fashionable. In the former case, it's pretty much a gamble but you might actually get something out of it. In the later case all you're earning is the ability to slap another keyword on a resume that only mediocre HR people care about, being actually a time waist as it's keeping you from learning things that might actually be of interest for the things you're trying to accomplish (other than getting a shitty job of course).
Just as people that learned PHP or Java back in the day found out, learning for the sake of getting a job is a sure way to land you a shitty and boring job in which you are replaceable cog. Managers love popular languages and frameworks, of course they do. And the interesting jobs that are out there, that make people happy and that pay well - well, let me tell you, those companies aren't looking for keywords on your resume, but for things that you've actually built.
And after some years from now, when you'll be over 40, you'll find yourself either a manager that does LinkedIn searches for keywords, or an obsolete developer that can't find a job because everything you've learned is obsolete and you waisted your time in learning syntax, instead of learning new abstractions, algorithms and mathematics - you know, stuff that never gets old.