It allows writing very fast code

Marco Alka This is a common misinformation.

At the current state of WASM, without SIMD and threading support, WASM runs as fast as JS in peak performance. Which means a JS code and it's equivalent WASM code will execute at the same peak performance.

You may want to watch this explanation to understand why ->

youtu.be/njt-Qzw0mVY

(WASM will eventually get more performance advantage when support for SIMD and Threading lands... but for now, the execution speed is a tie between JS and WASM)

Twaha Rahman

While it is true that SIMD and other benefits do help performance a lot, JS still has several big problems which hinder it performance-wise. Most of them stem from the flexibility JS gives us. Compiling to WASM allows writing very fast code and usually WASM files are way faster than similar JS code, because it lacks a lot of considerations. My statement is not wrong, and your YT video confirms that. I also dedicated my second paragraph to that. JS by itself is not slow :)

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!