Throttle a function to a fixed rate

// Throttle: allow one call per `wait` ms and keep the latest arguments.
function throttle(fn, wait, { leading = true, trailing = true } = {}) {
  let last = 0;
  let timer = null;
  let pending = null;

  function invoke(args) {
    last = Date.now();
    fn.apply(null, args);
  }

  function throttled(...args) {
    const elapsed = Date.now() - last;
    if (leading && elapsed >= wait) return invoke(args);
    if (!trailing) return;
    pending = args;
    if (timer) return;
    timer = setTimeout(() => {
      timer = null;
      const latest = pending;
      pending = null;
      if (latest) invoke(latest);
    }, Math.max(0, wait - elapsed));
  }

  throttled.cancel = () => {
    clearTimeout(timer);
    timer = null;
    pending = null;
    last = 0;
  };

  return throttled;
}

const log = throttle((value) => console.log('position', value), 100);
log(1); log(2); setTimeout(() => log(3), 250); // 1, then 2 at ~100 ms, then 3