A first custom hook in React
React interview exercise on Custom hooks, difficulty 1 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write useToggle(initial = false) returning [on, toggle, setOn] as a tuple: `toggle` flips the value, `setOn` sets it. `toggle` must be the same function on every render (useCallback), so it can be passed to memoized children.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.