JavaScript.info
javascript.info
A comprehensive and modern JavaScript tutorial covering the language from fundamentals to advanced topics — prototypes, async/await, closures, generators, and the DOM — with interactive exercises throughout.
Why it is useful
The best free JavaScript reference that is both thorough and readable. Unlike MDN (which is a reference, not a tutorial) or older resources still teaching ES5, this covers the modern language correctly with clear explanations and exercises that check your understanding. The chapters on prototypes, closures, and the event loop are particularly good — concepts most tutorials gloss over.