Yeah, it's available in the browser. I'm not even trying to slam JavaScript--I sort of like it for all of its foot-guns, but this is literally the only reason worth considering for its success.
Edit: I like several things about JS. Certainly if it didn't have first class functions, or easy object literals, that would be a pain. Likewise, if it didn't have insane implicit conversions and painful APIs, that would be great. But the good features didn't make JavaScript successful, just like the terrible features didn't kill it.
And Node was a function of JavaScript's ubiquity, not a cause. Having a server side platform will help keep momentum behind the language, but it really happened because JavaScript was already so big.
While it certainly has good points besides platform ubiquity, if you were trying to derive an equivalent of big-O for the popularity of javascript, language level criticisms and acclamations would count as, at best, linear concerns, where platform ubiquity is an exponential concern.
Platform ubiquity is so completely important in the determination that all other concerns can be ignored entirely.
Given a choice of supporting half of systems in javascript, and all systems in brainfuck, people would begin writing brainfuck-targeting compilers immediately.
The problem is this spurious inference drawn from package count to language superiority. In reality what's popular is targeting browsers, and there simply aren't any other languages with first-class support by browsers no matter how much we want them. This isn't a matter of Javascript being better than everything else, it's a matter of historical accident and network effects.
Node only came about b/c Google wrote V8 for high-performance browser JS. Node has certainly expanded JS's reach in a big way, but wouldn't have existed in the first place if, say, Lua were the lingua franca of all web browsers (or maybe V8 and Node would still exist but target Lua instead).
For all of JS quirks it is clearly getting something(s) very right.