WebAssembly Browser Support and Detection

WebAssembly Detection

WebAssembly (Wasm) enables near-native performance for computation-heavy tasks in the browser. It is a binary instruction format that runs in a sandboxed virtual machine alongside JavaScript.

Detection

const hasWasm = typeof WebAssembly !== 'undefined'
  && typeof WebAssembly.instantiate === 'function';

Streaming Compilation

Modern browsers support streaming compilation, which compiles Wasm modules while they are still downloading:

async function loadWasm(url) {
  if (WebAssembly.instantiateStreaming) {
    const { instance } = await WebAssembly.instantiateStreaming(
      fetch(url)
    );
    return instance;
  }
  // Fallback for older browsers
  const response = await fetch(url);
  const bytes = await response.arrayBuffer();
  const { instance } = await WebAssembly.instantiate(bytes);
  return instance;
}

Feature Tiers

Feature	Detection
Basic Wasm	typeof WebAssembly !== 'undefined'
Streaming	WebAssembly.instantiateStreaming
Threads	WebAssembly.Memory with shared: true
SIMD	Compile a SIMD test module
Exception handling	Compile a test module with try/catch

Performance Considerations

• Wasm code typically runs at 80-95% of native speed
• First load includes compilation time; subsequent loads use cached compiled modules
• Wasm and JavaScript can call each other, but boundary crossing has overhead
• Large Wasm binaries benefit from streaming compilation and lazy loading