About

An illustrated map of JavaScript.

JavaScript Codex is a free course that teaches JavaScript the way it's easiest to understand it — by drawing it. Every concept that has a shape in memory, a sequence in time, or a flow of data gets its own diagram, and the ones that move get an interactive animation you can step through.

What's inside

224 lessons across four parts, from your very first line of code to the parts of the platform most courses never reach:

• The Language — variables, types, functions, objects, prototypes, closures, classes, async/await, generators, plus the ES2023–2025 additions (immutable array methods, Object.groupBy, Set methods, iterator helpers, Temporal, and more).
• The Browser — the DOM, events, forms, and the modern interface APIs: observers, native dialogs and popovers, view transitions, the Navigation API, and accessibility.
• Advanced — the event loop, network, storage, Web Workers, Service Workers and PWAs, streams, security, performance, and graphics.
• Ecosystem & Tooling — modules and packages, build tools, testing, runtimes, and code quality.

How it's taught

Each lesson is written to serve a beginner and a returning professional in the same breath: a plain-language on-ramp first, the underlying mechanics next, and the sharp edges and gotchas last. Concepts are explained once and cross-linked everywhere they're needed, so nothing is repeated and nothing is assumed. Code examples are real and runnable; the diagrams are hand-built vector graphics that stay crisp at any zoom and adapt to light and dark themes.

Kept current

The web moves, and a course that teaches var and callbacks as the state of the art is worse than none. Lessons track the current language (through the latest finished ECMAScript proposals) and the current platform, with each feature's real-world browser support stated honestly — including when something is still emerging and needs a polyfill or a build step.

Ready to start? Open the course →