JavaScript Challenge

Feed your brain. Level up. Learn to write real JavaScript by solving one puzzle at a time, right on your phone. JavaScript Challenge is a single path of original coding problems, from your first function to graphs, dynamic programming and beyond. Every solution runs on-device in real JavaScript and is checked against hidden tests, so passing means it actually works. Free to start: the opening levels are free, then unlock the full path with a single one-time purchase. No subscription, no ads, no account. WRITE REAL CODE • A coder keyboard built for JavaScript: tab, brackets, quotes, snippets, undo • Instant feedback with named tests, expected vs actual output • Some levels enforce rules (no built-in array helpers, recursion required) so you learn the technique, not the shortcut LEARN THE RIGHT WAY • Three-tier hints from Rhino, your smug but surprisingly helpful mentor • Curated solutions after you solve: naive vs optimal, time and space complexity • Topics: strings, arrays, objects, closures, recursion, dynamic programming, sorting, searching, graphs, trees, hashing, bit tricks, grids, greedy strategies, intervals STAY MOTIVATED • One path, no shortcuts: easy → medium → hard, with performance tests on the hardest levels • XP, player levels, daily streaks and badges • Six themes, dark and light PRIVATE BY DESIGN • Works fully offline, no account, no tracking — your progress stays on your device • No ads, ever