[z3t4]

JavaScript is easy to debug and test, its relative safe, and closures makes it easy to write async programs. Compared to C or C++ you'll have a huge productivity boost with a very small performance penalty. It's also easy to learn compared to other languages. It also doesn't have a standard library which makes it easy to integrate into any platform. For example in Windows OS and other Microsoft products you've been able to use JavaScript as a scripting language for a very long time. So JavaScript is not a language that has only been available in browsers. There are actually people out there that prefer JavaScript and write in it voluntarily.

[lixquid]

Personally, I'd say Lua and its family of small, easy languages more easily fills those roles.

Not that I doubt some people do voluntarily enjoy JavaScript, but because of the sheer volume of StackOverflow questions, blog posts, micro-techologies, and other assorted attention bestowed upon the language it can be easy to make the logical jump that JavaScript the language is far more popular (in the satisfaction sense) than is actually so.