I always feel like I'm downloading megabytes of it whenever someone uses it. In practice it is. Even a basic hello world in rust will set you back a few megabytes compared to a the tens of bytes it takes in javascript.
>JavaScript comes with more of a standard library and more of a runtime, which unbalances comparisons.
Being able to make programs in a few bytes is a legitimate strength. You can't discount it because it's an effective way javascript saves size.
Lies. It’s 35 kB:
$ cargo new x
…
$ cd x
$ cat src/main.rs
fn main() {
println!("Hello, world!");
}
$ cargo build --release --target=wasm32-unknown-unknown
…
$ ls -l target/wasm32-unknown-unknown/release/x.wasm
… 34597 …
For the rest: I mention comparisons being unbalanced because people often assume it will scale at the rate they’ve seen—twice as much code, twice as much size. Runtimes and heavy tables make for non-scaling overhead. That 35 kB you’ve paid for once, and now can use as much as you like without further growth.
Meanwhile, an empty React project seems to be up to 190 kB now, 61 kB gzipped.
For startup performance, it’s fairly well understood that image bytes are cheap while JavaScript bytes are expensive. WebAssembly bytes cost similar to images.
That's definitely not true.
A debug build of a "hello wasm-bindgen" style Rust program indeed takes ~2MB, but most of that is debug into; disabling that and/or stripping gets it down to 45-80kB (depending how I did it). And a release build starts at 35kB, and after `wasm-opt -O` gets down to 25kB. AFAIK most of the remaining space is used by wasm-bindgen boilerplate, malloc and panic machinery.
...and then, running wasm-bindgen to generate JS bindings somehow strips most of that boilerplate too, down to 1.4kB.
Side note, I never understood how wasm-opt is able to squeeze so much on top of what LLVM already did (it's a relatively fast post-build step and somehow reduces our production binaries by 10-20% and gives measurable speedups).