Wasm Expert

• Compile Rust to Wasm with wasm-pack for browser targets (wasm-pack build --target web) or cargo build --target wasm32-wasi for server-side WASI modules
• Use wasm-bindgen to expose Rust functions to JavaScript and import JS APIs into Rust; annotate public functions with #[wasm_bindgen] and use JsValue for dynamic interop
• Define component interfaces in WIT files specifying exports (functions the component provides) and imports (functions the component requires from the host)
• Compose multiple Wasm components using wasm-tools compose, linking one component's imports to another's exports without source-level dependencies
• Optimize binaries with wasm-opt -Oz for size or -O3 for speed; use wasm-tools strip to remove custom sections and debug information for production builds
• Instantiate modules in the browser with WebAssembly.instantiateStreaming(fetch("module.wasm"), importObject) for the fastest possible startup
• Enable SIMD (Single Instruction, Multiple Data) for compute-intensive workloads by compiling with target features enabled and using explicit SIMD intrinsics or auto-vectorization

Common Patterns

• Plugin Architecture: Host application loads untrusted Wasm plugins with restricted WASI capabilities; plugins export a known interface (defined in WIT) and cannot access resources beyond what the host provides
• Polyglot Composition: Compile components from different languages (Rust, Go, Python) to Wasm components with WIT interfaces, then compose them into a single application using wasm-tools
• Streaming Compilation: Use WebAssembly.compileStreaming to compile the module while it downloads; pair with instantiate for near-zero wait time after the network transfer completes
• Memory-Mapped I/O: For large data processing in Wasm, share a linear memory region between the host and the module, passing pointers and lengths instead of copying data across the boundary

Pitfalls to Avoid

• Do not assume all WASI APIs are available in every runtime; WASI Preview 2 is still being adopted, and different runtimes (Wasmtime, Wasmer, WasmEdge) support different subsets
• Do not allocate memory freely without a strategy; Wasm linear memory grows in 64KB page increments and never releases pages back to the OS, so fragmentation accumulates over time
• Do not pass complex data structures across the Wasm boundary by serializing to JSON; use shared linear memory with well-defined layouts or the component model's typed interface for efficiency
• Do not skip testing on the target runtime; behavior differences exist between browser engines (V8, SpiderMonkey, JavaScriptCore) and server-side runtimes, especially for threading and SIMD