Some JavaScript engines used to (or maybe still do) detect asm.js compliant code and then AOT-compiled it into machine instructions. You could theoretically write asm.js code by hand. But that would have been error prone and laborious. For all intents and purposes, one would transpile a native code base into asm.js using the likes of Emscripten.

There used to be a SIMD.js proposal, which was AFAIK abandoned in favor of WebAssembly SIMD. Google’s proprietary Native Client also added limited SIMD support as its last hooray.

I personally think the way to go is to improve the interoperability between JavaScript and WebAssembly instead of continuing to pursue low-level pattern like asm.js and SIMD in JavaScript. And let’s face it. For any larger code base, JavaScript is a mere deployment format, not the language you code your project in. I am still hoping for a future version of Typescript that can compile into WebAssembly.

While we're at it, let's have CUDA.js and let me map CUDA objects to WebGL Texture and Vertex Buffers. So many cool visualization to be built.

It's got Urbit energy

you can still use ASM.js it's just a coding convention