Codable vs JavaScript Challenge

Codable turns programming practice into a habit. Solve focused challenges in ten languages — from your first data structure to lock-free concurrency — and build real fluency one problem at a time. WRITE REAL CODE IN 10 LANGUAGES C, C++, C#, Go, Java, JavaScript, Python, Rust, Swift, and TypeScript. Switch languages anytime — solve the same challenge in Python today and Rust tomorrow. GO DEEPER THAN SYNTAX Challenges span the topics that actually make you a better engineer: • Fundamentals and string manipulation • Data structures and algorithms • Recursion and functional programming • Object-oriented design and generics • Error handling, concurrency, and memory management BUILT FOR EVERY STAGE New to programming? Start with fundamentals and level up steadily. Experienced? Jump straight into concurrency, memory management, and the problems that show up in technical interviews. PRACTICE THAT STICKS Short, focused challenges designed to fit into a daily routine — because fluency comes from reps, not marathons. Download Codable and start mastering your chosen language!

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