[lixquid]

I'd wager a lot of this popularity is correlation, not causation. A lot of its popularity stems from being the dominant browser scripting language. This causes it to be popular with back-end frameworks for code re-use and shared developer skill. This causes it to be popular with, say, database engines that are used by the back-end, and so on and so forth.

WebAssembly is the first steps to truly breaking that chokehold, and truly seeing how popular JavaScript the language really is.

[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.

[BenoitEssiambre]

Right, however javascript will still be the only full featured language having its runtime and libraries included with the browser. That means that for other languages, only the ones with fairly light runtimes and libraries could be suitable for inclusion in most web apps. This will limit the choices for non javascript general development. It may be possible to do a webassembly/webgl rendering engine to replace html/css using a limited set of dependencies.

[akiselev]

Most news sources already load between 2 and 10 megabytes of Javascript, which is a significant fraction of, say, Python's runtime and many, many people browse those pages on mobile devices and connections without a problem. In Python's case, a large amount of the runtime size is taken up by all of the platform specific implementations of the standard library and they wouldn't work in the sandbox anyway.

Is there anything preventing Python.org from hosting the runtime environment on their CDN that everyone caches locally? Are there security issues from cross domain modules? Worst case, I don't think it would be hard to extend the LocalStorage API to cache modules between domains (perhaps with signed runtimes and a fallback).