Comment by noelwelsh
3 days ago
Speed is not fine. It's good enough for a lot of apps, but it doesn't get the job done for anything performance sensitive. An obvious issue is the lack of real machine number types, which makes anything numeric much slower than it could be.
Furthermore, JS semantics are limiting in other respects. E.g. there are people looking at tail calls and continuations in WebAssembly, which I can't see ever coming to JS.
> An obvious issue is the lack of real machine number types
This was basically what the special asm.js support in JS engines was about (via "use asm") and brought performance to about WASM level. IIRC this special asm.js support brought a 2x to 3x performance advantage (e.g. running asm.js in Chrome/Firefox which both had special asm.js support vs Safari which didn't).
AFAIK the initial WASM implementation in browsers was more or less an evolution of that asm.js special-path.