Comment by Marco Alka on "Is WebAssembly for Web developer?"

Yes. WebAssembly is for web devs. Is it an alternative for JS, though? Yes and no.

First of all, WASM is mostly useful for web apps. It allows writing very fast code, based on some guarantees WASM has and the structure it is delivered in. That's why it is ideal for compute-code, something JS is rather bad at.

However, does "JS is bad at compute" mean, that JS is slow, and we should write everything in WASM now, so that we can have uber-performance? No. JS is not slow. It is very adequate for most use-cases. Plus, as usual, if your program is slow, it's usually because of your code. Profile you application, identify the hot-path and the bottleneck and based on that write code which leads to a faster execution (for example use caching, lookup-tables, change the algorithm used, etc.). JS has a lot of advantages and most web devs are familiar with JS, so I would write a web-app with JS first.

WASM should only be considered if after optimization the application is still too slow, or libraries are required which are only available in a different language, are too much work to port and would perform subpar when transpiled to JS. In these cases, WASM can work wonders - at a prize.

WASM is one binary file. Hot-reloading code means replacing the whole blob, if at all supported (which means re-compiling all the code, which might take a moment)
WASM needs to be written in a typed language with available compiler - for example Rust, C++, Go, Lua, (a subset of) TypeScript, etc. (see list here) - which means learning a new language or at least all the subtle differences, as a team
Only the latest browsers support WASM (no accessibility, problems with corporate and special-machine usage, etc.)

On the bright side, we already have some tools which make life very easy, like the Parcel bundler if you need to extend a web-app, and a lot of frameworks in different ecosystems (I know at least about a lot of Rust crates, like the Amethyst game framework/engine) which are written with WASM in mind, if you want to create an app and need to bring it to the browser.

Marco Alka There's a few things, you're mistaking. I'll try my best to pint those out ->

JS by itself is not slow :)

JS is slow because it's a higher level lang with GC. The GC pauses hinder JS's execution speed.

The sole reason JS is as fast as WASM in peak execution speed is because of JS's JIT support.

Compiling to WASM allows writing very fast code and usually WASM files are way faster than similar JS code

I am assuming that by allows writing very fast code you mean allows executing code very fast.

But this is another misinformation. WASM files are executed by the same engine that executes JS JIT code.... thus their peak performance is the same. The reason why I'm saying peak performance is that JS being a higher level language has to stop code execution for GC cycles, which hinders JS's (JIT) overall perf.

WASM files are way faster than similar JS code

It depends. As I already have said, both JS and WASM have the same peak performance.

But if you were to compile another higher level language to WASM, take for example Python, then it would execute code at a slower speed than JS. So it depends what you compile to WASM. Just plainly compiling anything to WASM won't increase its execution speed.

(Btw... you can't compile Python into WASM yet as WASM still doesn't have a GC yet. There's currently a proposal for the GC but it won't support any lang fully. Only partial implementation of a few given languages will be supported by that GC. It's possible to compile and bring the whole Python GC but.... that will increase bundle size a LOT and you're still getting slower execution speed.)

WASM files are quickly parsable as they can be parsed while they are being steamed in through the network thanks to WebAssembly.instantiateStreaming. This is a HUGE advantage over JS, as JS files has to download fully and parsed before they can be executed. It also takes some time before the JS JIT kicks in. Do you mean this by saying, WASM files are way faster than similar JS code?

Anyawy.... glad to see a fellow Rustacean on the web. Cheers!

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