Js gained wide adoption thanks to favorable comparison on specific traits when compared to other languages.
- lower barrier to entry as far is toolchain setup is concerned. Nothing to install to build a Hello world.
- no weird concepts to grasp at first: many commonalities with other languages, meaning you don't start the learning curve with a big step.
I could go on but the gist is that JS is kind of like the pop music of programming languages: easy to like, with room to grow (as opposed to Justin Bieber or Miles Davis who miss one of these traits.)
To the question of what will be the next "buzz" (Js is a buzz, but those have different timelines and emotional loads than "leave Britney alone") the answer is:
Something even easier to grasp and access with a barrier to entry, smoother learning curve and wider applications.
It might even be an abstraction like those of Brett Victor.
I'd say that's not so much the language but what it allows beginners to achieve that is wave-defining.
Development has become mainstream and JS is the Pop Music of our days.