事件防抖

function debounce(fn, delay) {
  let timer
  return function (...args) {
    if (timer) {
      clearTimeout(timer)
    }
    timer = setTimeout(() => {
      fn.apply(this, args)
    }, delay)
  }
}
// 测试
function task() {
  console.log('run task')
}
const debounceTask = debounce(task, 1000)
window.addEventListener('scroll', debounceTask)