WebAssembly is a special encoding for a subset of javascript that's easier to optimize. If all arbitrary javascript could be compiled to WebAssembly and get any

WebAssembly is a special encoding for a subset of javascript that's easier to optimize. If all arbitrary javascript could be compiled to WebAssembly and get any benefit, then browsers wouldn't bother with asmjs/WebAssembly and would just implement those optimizations in their general Javascript engines. WebAssembly is a good compilation target for languages with a flat memory space and no garbage collection.