wtfjavascript

WTF, JavaScript?! — 150+ advanced JavaScript challenges in your terminal.

Coercion nightmares ([] == ![], the == algorithm, c == 1 && c == 2 && c == 3), closures and higher-order functions, Proxy traps, floating-point money math, sorting algorithms, BFS/DFS, LeetCode-style interview classics, and brutal "what does this log?" quizzes — each with a hint naming the exact method to reach for, judged locally in a sandbox.

Install

npm install -g wtfjavascript
# or with Bun (same registry, fully supported — the sandbox judge runs under Bun too)
bun add -g wtfjavascript
# or zero-install
npx wtfjavascript
bunx wtfjavascript

Play

wtfjs                              # randomized exam (8 challenges)
wtfjs --count 5                    # shorter run
wtfjs --topic "Proxy & Reflect"    # single topic
wtfjs --list                       # list every challenge
wtfjs --server https://wtfjavascript.dev   # record your run on the leaderboard

Coding challenges open your own $EDITOR — write the solution, save, close, and the judge runs the hidden tests plus source constraints (e.g. must use .some(), no temp variable). r dry-runs your code and shows console.log output without spending a try; h reveals the hint.

Zero dependencies — plain Node.js (≥18).

The full experience

The web app at wtfjavascript.dev has the same challenge bank with a CodeMirror editor, drag-and-drop ordering problems, animated visuals, exam mode, and a persistent leaderboard.