JavaScript › Memory Management & Garbage Collection

Why can setInterval() be a subtle source of memory leaks, and how do you avoid it?

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Answer

A running setInterval() keeps its callback (and everything it closes over) alive indefinitely until clearInterval() is called — if the component or context that started it is destroyed without ever clearing the interval, the callback and its retained scope leak for the rest of the page's lifetime.

function startPolling() {
  const largeState = loadInitialState();
  const id = setInterval(() => checkStatus(largeState), 1000);
  return () => clearInterval(id); // must be called on cleanup
}

Real-world example A React component that starts a setInterval() in useEffect but forgets to return a cleanup function calling clearInterval().

Common follow-ups: Does the same leak risk apply to setTimeout() used for repeated polling via re-scheduling itself?

Event Loop & Concurrency