WebAssembly (Wasm) is a binary format that runs in the browser at near-native speed. It lets you take code written in languages like Rust, C, C++, or Go and run it in a web page.

JavaScript is great, but it’s slow for heavy computation — image processing, video editing, 3D games, encryption. WebAssembly fills that gap.

How it works

1. You write code in Rust, C, C++, or Go
2. You compile it to a .wasm binary file
3. Your JavaScript loads and runs the .wasm file in the browser
4. The browser executes it at near-native speed

// Load and run a WebAssembly module
const response = await fetch('module.wasm');
const { instance } = await WebAssembly.instantiateStreaming(response);

// Call a function defined in Rust/C
const result = instance.exports.fibonacci(40);

JavaScript vs WebAssembly

	JavaScript	WebAssembly
Speed	Fast (JIT compiled)	Faster (pre-compiled)
Use case	UI, DOM, general logic	Heavy computation
Languages	JavaScript/TypeScript	Rust, C, C++, Go, etc.
DOM access	Direct	Through JavaScript
File size	Text (larger)	Binary (smaller)

WebAssembly doesn’t replace JavaScript — they work together. JavaScript handles the UI and DOM, WebAssembly handles the heavy lifting.

Real-world examples

• Figma — the design tool runs C++ compiled to Wasm for performance
• Google Earth — 3D rendering in the browser
• Photoshop Web — Adobe ported parts of Photoshop to Wasm
• AutoCAD — runs in the browser via Wasm
• Game engines — Unity and Unreal can export to Wasm
• SQLite — runs entirely in the browser as Wasm

When to use WebAssembly

• ✅ CPU-intensive tasks (image/video processing, compression)
• ✅ Porting existing C/C++/Rust code to the browser
• ✅ Games and 3D graphics
• ✅ Cryptography and hashing
• ✅ Scientific computing and simulations
• ❌ Simple web apps (JavaScript is fine)
• ❌ DOM manipulation (Wasm can’t access the DOM directly)
• ❌ Small scripts (the overhead isn’t worth it)

Getting started with Rust + Wasm

Rust has the best WebAssembly tooling:

# Install the Wasm target
rustup target add wasm32-unknown-unknown

# Install wasm-pack (builds Rust → Wasm with JS bindings)
cargo install wasm-pack

# Create a new project
cargo new --lib my-wasm-project

// src/lib.rs
use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn fibonacci(n: u32) -> u32 {
    if n <= 1 { return n; }
    fibonacci(n - 1) + fibonacci(n - 2)
}

wasm-pack build --target web

Beyond the browser

WebAssembly also runs outside the browser:

• Edge computing — Cloudflare Workers uses Wasm
• Serverless — Wasm containers start in milliseconds (vs seconds for Docker)
• Plugins — Envoy, Istio, and other tools use Wasm for extensibility