asmjs is going to be strictly more limited in interacting with JS than wasm. You're basically limited to simple number values and array buffers. Whereas wasm now a days has GC types and can hold onto JS value using externref.
> But more important for what i was trying to do, you can't zero copy buffers from js to wasm
I'm pretty sure you can't do that with asmjs either. There is a proposal for zero-copy buffers with wasm: https://github.com/WebAssembly/memory-control/blob/main/prop...
Had WASM not been adopted we would have SIMD in JS ( probably via asm.js) by now. Because we didn't, JS just cannot compete with WASM in many computationally heavy workflows. We'd also have general purpose JS to Asm.js compilation, with few API restrictions, making writing it much easier.
WASM is that evolution of (strict mode) asm.js. The two really aren't all that different from what they can and can't do.
But since asm.js is just (a subset of) javascript, I assumed I could just pass ArrayBuffers around.
With wasm, I could pass a Uint8Array out of it. If I wanted to pass it in, I had to call malloc from the javascript side to allocate in the wasm heap. But since I already had an arraybuffer (from a file upload), that meant an extra copy.
> You can't call most web apis from wasm.
You can't from strict asm.js either, since it only supports numbers (no JS strings or objects) and manages the C heap in an ArrayBuffer object just like WASM.
> But more important for what i was trying to do, you can't zero copy buffers from js to wasm.
Same problem as above, you need to call out into "real" Javascript from asm.js and you can't map other ArrayBuffers directly into the 'asm.js heap' either, a copy is needed. The "Javascript FFI" really isn't much different between asm.js and WASM.
AFAIK as soon as you'd start mixing idiomatic JS and asm.js, you lose the "special sauce", you only got the special asm.js treatment in browsers when putting a "use asm" at the top of a source file, and that would prevent using regular JS features in the same file.
> An asm.js module can take up to three optional parameters, providing access to external JavaScript code and data:
> - a standard library object, providing access to a limited subset of the JavaScript standard libraries;
> - a foreign function interface (FFI), providing access to custom external JavaScript functions; and
> - a heap buffer, providing a single ArrayBuffer to act as the asm.js heap.
From http://asmjs.org/spec/latest/#introduction:~:text=External%2...
In asm.js you have to treat JS functions and objects as special extern values, just like in WASM.
asm.js - when validated and optimized - is closer to WASM serialized to a JS-like syntax than actual JS.