WebAssembly Best Practices
Rules for WASM modules with clear interop boundaries and minimal payload size.
How to Use This List
- Apply before shipping WASM to production browsers or edge runtimes
- Treat every JS boundary crossing as a performance and ABI contract
- Measure wasm file size gzipped, not just raw bytes
A - Boundary Design
- Batch work per exported function. Amortize JS/WASM call overhead.
- Return owned data. Prefer
Vec<u8>/Stringover long-lived borrows. - Map errors to host types.
Result<JsValue, JsValue>in browsers; integer codes in WASI. - Avoid panics in exports. Use
console_error_panic_hookin dev only.
B - Size and Build
- Release profile tuned for size.
opt-level = "s", LTO,panic = "abort". - Run wasm-opt in CI. Track size regressions on every merge.
- Minimal web-sys features. Enable only APIs you import.
- Audit dependency tree.
default-features = falsewhere possible.
C - Runtime Behavior
- Await init() before calls. Document startup in README and TS types.
- Respect single-thread default. Use threads only when SharedArrayBuffer is available.
- Preallocate buffers. Reduce WASM memory growth in hot loops.
- Serve correct MIME type.
application/wasmwith compression.
D - Security and Ops
- Validate all host input. Treat JS strings and byte slices as untrusted.
- CSP compatible loading. Avoid
eval; use module imports. - Pin toolchain versions.
wasm-bindgen, wasm-pack, and Rust channel in CI. - Source maps for dev only. Do not ship full debug symbols to prod CDN.
E - Architecture Choices
- Rust for compute, JS for DOM glue. Unless team commits to Leptos/Yew fully.
- Choose target deliberately.
wasm32-unknown-unknownvswasm32-wasivs components. - Fallback path. Graceful degradation when WASM fails to load.
- SSR when SEO matters. Client-only WASM pages index poorly.
FAQs
When is WASM worth it?
CPU-heavy, portable logic: parsers, crypto, simulations, image/audio codecs.
Maximum module size?
Keep auxiliary modules under ~100 KB gzipped; split larger apps into lazy chunks.
How many exports?
Few coarse-grained exports beat dozens of tiny functions called in tight loops.
Testing strategy?
Unit test logic on native target; wasm-bindgen-test for browser-specific code.
WASI in production?
Growing for edge and plugins. Confirm runtime support before betting the architecture.
Component model now?
Adopt for new polyglot plugin boundaries; keep wasm-bindgen for existing browser apps.
Memory limits?
Browser tabs cap WASM memory. Stream large data instead of loading entirely into linear memory.
Debugging production?
Structured logging to host console; source maps in staging only.
Versioning WASM API?
Semver npm package; breaking export changes bump major version.
Accessibility?
If UI is WASM-rendered, manage focus and ARIA like any SPA framework.
Related
- WebAssembly Basics - fundamentals
- Performance & Size - optimization techniques
- wasm-bindgen - interop patterns
- wasm-pack & Bundling - shipping workflow
Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.