What are debounce and throttle? When do you use each?

• Debounce — fires AFTER user stops triggering. Best for: search input, resize, form validation
• Throttle — fires at most once per interval. Best for: scroll, mouse move

function debounce(fn, delay) {
  let timer;
  return (...args) => {
    clearTimeout(timer);
    timer = setTimeout(() => fn(...args), delay);
  };
}
const onSearch = debounce((q) => fetchResults(q), 300);