WebAssembly Integration Patterns for Web Apps

CPU-intensive tasks in JavaScript (image processing, crypto, parsing, simulations) block the main thread and cause janky UI.

Offload heavy computation to WebAssembly:

// Loading and using a WASM module
async function initWasm() {
  const response = await fetch('compute.wasm');
  const bytes = await response.arrayBuffer();
  const { instance } = await WebAssembly.instantiate(bytes, {
    env: {
      log: (ptr, len) => console.log(readString(ptr, len)),
    }
  });
  return instance.exports;
}

// Using with a Web Worker (don't block main thread)
// worker.js
let wasm;
self.onmessage = async ({ data }) => {
  if (!wasm) wasm = await initWasm();
  const result = wasm.processImage(data.imagePtr, data.width, data.height);
  self.postMessage({ result });
};

// Main thread
const worker = new Worker('worker.js');
worker.postMessage({ imageData });
worker.onmessage = ({ data }) => updateCanvas(data.result);

Toolchains:

• Rust: wasm-pack + wasm-bindgen (best DX)
• C/C++: Emscripten
• Go: built-in WASM target
• AssemblyScript: TypeScript-like syntax

Use cases where WASM shines:

• Image/video processing
• Cryptography
• Physics simulations
• PDF generation
• Compression/decompression

WASM runs at near-native speed (typically 1.5-2x native C). For computation-heavy tasks, it can be 10-100x faster than equivalent JavaScript.

Optimizing CPU-intensive web applications