WebAssembly itself doesn't have anything to do with asm.js near as I can tell. It's more the ecosystem surrounding WebAssembly. I looked through the specs a l

WebAssembly itself doesn't have anything to do with asm.js near as I can tell. It's more the ecosystem surrounding WebAssembly. I looked through the specs a little bit. What it is, is a binary encoding of the AST with some optimizations thrown in to decrease size (symbol tables instead of using the full tokens). I'm unclear on why asm.js is even mentioned but I suspect it is a temporary stop gap since those languages using LLVM currently target asm.js. Now, they can just target the AST but it will take some time for the tools to change. In the meanwhile they will look like: C -> AST -> asm.js -> AST -> binary. In the future, it can just look like C -> AST -> AST -> binary. Why is it significant? 1) Language designers can just target the AST, then pass that to WebAssembly to compile to a binary. There's no need to compile to JavaScript. It saves them a step. 2) Size. They are claiming 20-30% smaller than minimized gzip versions of Javascript. There are optimizations that can be done (at the AST level) that exceed what is possible with generic compression like gzip. 3) Load time. Since it can be decoded straight to the AST, it saves the Javascript parsing step. This results in faster page loads. 4) Non-Javascript tooling support will improve. Javascript will still be the canonical language but other languages will increasingly get first class tooling support.