手写防抖debounce

const input1 = document.getElementById('input1')
  
  function debounce (fn, delay = 500) {
    let timer = null
    return function () {
      if (timer) {
        clearTimeout(timer)
      }
      timer = setTimeout(() => {
        fn.apply(this,arguments)
        timer = null   //释放空间                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
      }, delay)
    }
  }

  input1.addEventListener('keyup', debounce(function () {
    console.log(input1.value)
  }, 1000))