js防抖常用封裝

function debounce(func, wait, immediate) {
  let timeout, args, context, timestamp, result

  const later = function() {
    // 據上一次觸發時間間隔
    const last = +new Date() - timestamp

    // 上次被包裝函式被呼叫時間間隔 last 小於設定時間間隔 wait
    if (last < wait && last > 0) {
      timeout = setTimeout(later, wait - last)
    } 
 
else {
      timeout = null
      // 如果設定為immediate===true，因為開始邊界已經呼叫過了此處無需呼叫
      if (!immediate) {
        result = func.apply(context, args)
        if (!timeout) context = args = null
      }
    }
  }

  return function(...args) {
    context = this
    timestamp = +new Date()
    const callNow 
 
= immediate && !timeout
    // 如果延時不存在，重新設定延時
    if (!timeout) timeout = setTimeout(later, wait)
    if (callNow) {
      result = func.apply(context, args)
      context = args = null
    }

    return result
  }
}