Asking out of ignorance!
- It's low level like C and C++ so it maps cleanly onto WASM
- In your average Rust project, all dependencies are already built from source, greatly increasing the likelihood all your dependencies can be built for WASM
- Already using LLVM as the compiler backend made WASM targeting a lot less work than for languages that need to do that work from scratch
- Probably most importantly, a lot of developers involved in core rustc development were motivated to get Rust working on WASM
At least that's my perception for how Rust became such a prominent language for WASM development early on
The solution other languages targeting wasm typically use is bundling their own garbage collector in the compiled code, which of course adds a bit of code bloat. E.g. C# blazor wasm applications are not exactly small for this reason.
There was a message yesterday in the Kotlin slack about them starting work on a wasm compiler backend for Kotlin (they already have java, native, and js compilers). https://github.com/JetBrains/kotlin/tree/master/compiler/ir/... Interestingly they plan to depend on the wasm GC proposal instead of bundling their own: https://github.com/WebAssembly/gc/
So, things are improving on this front. But it's a big reason why Rust is particularly popular for wasm right now because they have no GC and lots of developer tools that are relatively mature because they've been working on this for a while.
IMHO, this will take another few years to fully mature but inevitably lots of people are going to be writing web applications that don't involve any or very little javascript. Kotlin is starting to look very solid for any kind of cross platform Android, IOS, and web based development (as well as server development, which is what I do). Swift would be another candidate and there already is a wasm compiler for that as well.
That is only the case for open source code like crates.io, there is nothing that guarantees you will get the source code of a third-party, though.
I mention this because in the native world it is common to give customers precompiled libraries.
> - Already using LLVM as the compiler backend
Some people don't seem to know this, but all languages that target LLVM (including C, C++, Fortran, Ada, Julia, Swift and others) can be used in WebAssembly.
Having LLVM doesn't mean that webassembly Just Works, in the same way that having LLVM doesn't mean that all of its architectures Just Work. And even after getting past the "hello world" stage, there's a lot of other work to do to make it more than just a toy.
Let's take Ada, for example. https://blog.adacore.com/use-of-gnat-llvm-to-translate-ada-a... talks about how to use Ada to build stuff for wasm, but you need to include https://github.com/godunko/adawebpack/ to make things work well. Someone had to write that code.
