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Rust and WebAssembly

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Rust and WebAssembly

Rust is one of the best-supported languages for WebAssembly development, thanks to its lack of a garbage collector, small runtime, and predictable performance characteristics. The Rust and WebAssembly working group maintains tooling and documentation to make this integration seamless.

Why Rust for WebAssembly?

  • No garbage collector: Produces small, efficient Wasm binaries without runtime overhead
  • Memory safety: Rust’s ownership model prevents bugs that are hard to debug in Wasm
  • Small binary size: Rust can produce minimal Wasm modules with #[no_std] and careful dependency management
  • Mature toolchain: First-class wasm32-unknown-unknown compilation target via rustup
  • Strong ecosystem: Libraries like wasm-bindgen, web-sys, and js-sys provide ergonomic JavaScript interop

Key Tools

  • wasm-pack - One-stop shop for building, testing, and publishing Rust-generated Wasm packages
  • wasm-bindgen - Facilitates high-level interactions between Rust and JavaScript
  • web-sys - Bindings to Web APIs (DOM, Canvas, Fetch, etc.)
  • js-sys - Bindings to JavaScript built-in objects and functions
  • wee_alloc - A tiny allocator for size-conscious Wasm modules

Typical Workflow

  1. Create a new Rust library with cargo new --lib
  2. Set crate-type = ["cdylib"] in Cargo.toml
  3. Add wasm-bindgen as a dependency
  4. Write Rust functions annotated with #[wasm_bindgen]
  5. Build with wasm-pack build
  6. Import the generated package in JavaScript/TypeScript

Example

use wasm_bindgen::prelude::*;
 
#[wasm_bindgen]
pub fn greet(name: &str) -> String {
    format!("Hello, {}!", name)
}

Use Cases

  • Performance-critical web features: Image processing, video encoding, physics simulations
  • Porting existing Rust libraries to the web
  • Shared logic between server (native Rust) and client (Wasm)
  • Edge computing with Wasm runtimes (Cloudflare Workers, Fastly Compute)

Resources

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