Crack JavaScript. Put your code and DevTools skills to the test.

Write functions, predict output and solve puzzles in browser developer tools. Practice at your own pace, with nothing to install.

Puzzles: 266 · Without an account: 9 · Difficulty levels: 5

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Medium

Truthy and default values

What does the code print? Compare boolean conversion with || and ??. Enter one line with | separators.

console.log([Boolean('0'), Boolean(0), Boolean([]), 0 || 7, 0 ?? 7].join('|'));

For JavaScript learners who know the basics, developers and testers. Pick a skill and start with a warm-up.

Write functions, fix bugs and test your solutions. Practice reading code and solving problems.

Predict output, understand type conversions and work out the order of asynchronous operations.

Find hidden values, inspect headers and modify HTTP requests in purpose-built puzzles.

Scenarios from real applications: carts, API data, reservations, permissions and file imports. Pick a level and solve a concrete problem.

Challenges in this category: 55 · Available without an account: 2

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