useInterval

Requirements

• Export useInterval(callback, delay) as a named and default React hook. Return undefined. In TypeScript use callback: () => void and delay: number | null.
• For a finite nonnegative numeric delay, create one repeating interval. The first callback occurs asynchronously after an interval delay; never call it during rendering. Zero is a valid asynchronous interval.
• delay = null pauses the interval. A change from null to a number starts a new interval; changing a numeric delay removes the previous interval and starts one with the new delay.
• Always invoke the callback from the latest committed render. Changing only the callback must not clear or recreate the running interval or reset its timing.
• Unrelated rerenders must not restart the interval. Clean up the active interval on unmount and prevent duplicates under React Strict Mode effect replay.
• Instances must operate independently. A callback may schedule React state updates. Invalid delays, throwing callbacks, catch-up scheduling, async overlap prevention, and drift correction are outside scope.
• Use real React effects and refs. Browser scheduling determines the precise execution time; callers must not depend on exact millisecond precision.

Examples

Input: useInterval(() => setCount(count => count + 1), 1000)
Output: Increments count approximately once per second while mounted.

Input: Rerender with delay = null
Output: Stops future ticks until resumed.

Input: Rerender with a new callback and the same delay
Output: The next tick uses the new callback without creating a new interval.