Task: write debounce

Debounce delays running a function until no further call arrives for a given time. Below is the trailing version, with no call at the start of a burst.

function debounce(fn, wait) {
  let timer;
  function wrapped(...args) {
    clearTimeout(timer);
    timer = setTimeout(() => fn.apply(this, args), wait);
  }
  wrapped.cancel = () => clearTimeout(timer);
  return wrapped;
}

To be precise: a regular function keeps the caller's this; the timeout closes over the latest arguments. On cleanup I call cancel.

Pitfall: creating a new debounced function on every event means the timer can't be shared. This is the basic interview version, without leading, maxWait or returning a Promise.