WebAssembly 101 – High-Performance Web Apps

Note: This article was originally published on June 12, 2018. Some information may be outdated.

WebAssembly (Wasm) is a low-level bytecode format designed to run code at near-native speed in modern browsers. It allows developers to compile code from languages like C, C++, or Rust and execute it on the web alongside JavaScript.

WebAssembly reached its 1.0 release and was supported in all major browsers, marking a big step toward making the web a platform for high-performance apps.

What is WebAssembly?

WebAssembly is:

• A binary format for the web
• Designed for speed and efficiency
• Executed in a safe, sandboxed environment
• Meant to work alongside JavaScript

It’s not meant to replace JavaScript, but to handle tasks where performance is critical--like image manipulation, games, simulations, or video editing.

Why WebAssembly Matters

• It allows reuse of existing C/C++/Rust codebases on the web.
• It dramatically improves performance for CPU-intensive tasks.
• It expands what’s possible in the browser.

Basic JavaScript Interop

Once a .wasm file is compiled, you can load and run it with JavaScript:

const fs = require("fs");

const wasmBuffer = fs.readFileSync("./example.wasm");

WebAssembly.instantiate(wasmBuffer).then(wasmModule => {
  const result = wasmModule.instance.exports.add(10, 15);
  console.log(result); // 25
});

A Simple Example in C

This C code compiles to WebAssembly:

int add(int a, int b) {
  return a + b;
}

You can use a tool like Emscripten to compile it:

emcc add.c -s WASM=1 -o add.wasm

Then call it from JavaScript as shown above.

Use Cases

• Game engines and emulators
• Real-time audio/video processing
• Image processing
• Scientific simulations
• Running existing C/C++ libraries in the browser

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WebAssembly opened up a new world of performance for the web. It’s not just for C++ developers--it’s a tool that front-end devs can use to unlock new capabilities.

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Originally published at letanure.dev