防抖函数

function debounce(fn, delay = 300, immediate = false) {
  let timer = null;
  return function (...args) {
    if (timer) clearTimeout(timer);
    if (immediate && !timer) {
      fn.apply(this, args);
    }
    timer = setTimeout(() => {
      timer = null;
      if (!immediate) fn.apply(this, args);
    }, delay);
  };
}