onMounted and onUnmounted in Vue
Vue interview exercise on Lifecycle & refs, difficulty 2 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 Ticker with props `every` (ms, default 1000) and `onTick` (function): count ticks in a ref shown as <output>N</output>, start a setInterval on mount that increments the count and calls onTick with the new count, and clear it on unmount so nothing runs afterwards.
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.