Lambda guides you through Closure Caves. Standing in the way: The Mutator — every mistake this lane teaches you to avoid. Functions, objects, arrays, classes, modules, gotchas and every ES version — the deep language arts.
All 61 lessons below are free, need no signup, and each one opens as a comic issue with a live try-it sandbox, a task list that pays XP, and a narrator that reads it aloud. Progress is stored in your own browser — nothing is uploaded anywhere.