A Practical Guide to WebAssembly Basics
A binary format that lets code written in languages such as C++ or Rust run in the browser at near-native speed.
Marcus Adeyemi
What is at stake
WebAssembly suits heavy computation such as image processing and simulations, but it is not a replacement for JavaScript.
The playbook
- Use WebAssembly for compute-heavy work
- Keep modules small and lazy loaded
- Measure against a JavaScript implementation
- Handle load failures gracefully
- Watch memory use on mobile
Where it goes wrong
Avoid:
- Rewriting interfaces in WebAssembly
- Large modules on first load
- Assuming automatic speed gains
- Ignoring fallbacks
The numbers behind it
| Measure | Figure |
|---|---|
| Format | a portable binary instruction format |
| Interop | WebAssembly modules are called from JavaScript |
| DOM access | modules access the page through JavaScript |
| Size | modules add to download weight |
Getting outside help
When to hand it over: Bring in help when browser-side computation is a bottleneck.
Where this comes from
- MDN Web Docs — WebAssembly
- web.dev — WebAssembly
The figures and practices above come from the sources listed.
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Where to go next
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