Intro: What Is WebAssembly?

WebAssembly (Wasm) is a portable binary instruction format designed for a stack-based virtual machine. It is not a programming language you write by hand in production — it is a compilation target: a compact, validated binary that browsers, servers, and edge runtimes can load and execute at near-native speed.

Think of it the way you think of bytecode in the JVM or CLR, except it is designed to be vendor-neutral and run anywhere — in Chrome, Firefox, Safari, Node.js, Deno, Cloudflare Workers, and beyond.

What This Course Covers

This course takes you from zero familiarity to confident Wasm practitioner. Here is what each module covers:

Module	Topic
1 — Intro	What Wasm is, the binary/text duality, the stack VM model
2 — WAT Text Format	Writing WebAssembly Text format by hand to understand the fundamentals
3 — JS Interop	Calling Wasm from JavaScript and passing data back and forth
4 — Linear Memory	How Wasm’s flat memory model works and how to share it with JS
5 — Languages to Wasm	Compiling Rust, C/C++, and AssemblyScript to .wasm
6 — Tooling	wasm-pack, wasm-bindgen, emcc, optimization, debugging
7 — WASI	The WebAssembly System Interface — running Wasm outside the browser

How Source Code Becomes a .wasm Binary

Every .wasm file starts life as source code in a higher-level language. A compiler reads that source and emits the compact binary that the runtime loads directly.

flowchart LR
  A["Rust / C / C++ / AssemblyScript"] --> B["Compiler\n(rustc / emcc / asc)"]
  B --> C[".wasm binary"]
  C --> D["Browser\n(JS + Wasm API)"]
  C --> E["Server / Edge\n(Node.js / WASI)"]

Source language → compiler → .wasm binary → runtime

Try It Now

Even in this very first lesson you can run real WebAssembly. The runner below compiles a tiny WAT module that returns the answer to life, the universe, and everything.

WebAssemblyRun ▸Open in StackBlitz ▸

const wat = `(module (func (export "answer") (result i32) i32.const 42))`; const bytes = await compileWat(wat); const { instance } = await WebAssembly.instantiate(bytes, {}); console.log('answer() =', instance.exports.answer());

🦾 Wasm is a compilation target

You almost never write Wasm by hand in production. Instead you write Rust, C, C++, AssemblyScript (or WAT for learning) and compile to a compact .wasm binary. The browser or server loads the binary directly.

What is WebAssembly?

A new programming language replacing JavaScript A portable binary instruction format for a stack-based virtual machine A JavaScript framework for web apps A browser-specific scripting language

In production, .wasm binaries are typically produced by...

Writing WAT by hand Compiling from a higher-level language like Rust or C Transpiling JavaScript Downloading from npm

Where can WebAssembly run?

Only in Chrome Only in browsers In browsers and server/edge runtimes Only on Linux servers

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