SOURCE

function throttle(fn, delay, options = { leading: true, trailing: true }) {
  let timer = null;
  let previous = 0;

  return function (...args) {
    const now = Date.now();

    if (!options.leading && previous === 0) {
      previous = now;
    }

    const remaining = delay - (now - previous);

    if (remaining <= 0) {
      if (timer) {
        clearTimeout(timer);
        timer = null;
      }
      previous = now;
      fn.apply(this, args);
    } else if (!timer && options.trailing) {
      timer = setTimeout(() => {
        previous = options.leading ? Date.now() : 0;
        timer = null;
        fn.apply(this, args);
      }, remaining);
    }
  };
}

const throttledFn = throttle(() => {
  console.log('触发了', Date.now());
}, 2000, { leading: true, trailing: true });

window.addEventListener('scroll', throttledFn);