It’s by now a cliché that JS has become the assembly language of the Web. Rather, JS is one syntax for a portable and safe machine language, let’s say. Today I’m pleased to announce that cross-browser work has begun on WebAssembly, a new intermediate representation for safe code on the Web - brendaneich.com 
What: WebAssembly, “wasm” for short, .wasm filename suffix, a new binary syntax for low-level safe code, initially co-expressive with asm.js, but in the long run able to diverge from JS’s semantics, in order to best serve as common object-level format for multiple source-level programming languages.
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A source-to-source compiler, transcompiler or transpiler is a type of compiler that takes the source code of a program written in one programming language as its input and produces the equivalent source code in another programming language - wikipedia
How: If you use Emscripten, then wasm support via a command-line flag will at first include and target the prototype polyfill.