The 4 major browsers have come together to create WebAssembly (https://blog.mozilla.org/luke/2015/06/17/webassembly/), a binary compilation target for the web. This is very exciting news.
I see this as something like JVM for browsers. While not everyone loves Java, most people have really good things to say about JVM. You can compile your language down to Java bytecode and have it run everywhere. A major limitation of many languages is that it only runs where there is a virtual machine built for it. By compiling down to Java bytecode, the language can run anywhere.