节流与防抖

防抖或是节流：限制函数的执行次数

1. 防抖：在一定的时间间隔内，将多次触发变成一次触发；

2. 节流：减少一段时间的触发频率；

防抖函数 (debounce)

const debounce = (fn, wait = 500) => {
  let timer = null
  return function (...args) {
    if (timer) clearTimeout(timer)
    timer = setTimeout(fn.bind(this), wait, ...args)
  }
}

节流函数 (throttle)

const throttle = (fn, wait = 500) => {
  let timer = null
  return function(...args) {
    if (timer) return
    timer = setTimeout(fn.bind(this), wait, ...args)
    timer = null
  }
}