code: function after (count, callback, context) {
    var runCount = 0
    var rests = []
    context = context || this
    return function () {
      runCount++
      if (runCount <= count) {
        rests.push(arguments[0])
      }
      if (runCount >= count) {
        callback.apply(context, [rests].concat(arraySlice(arguments)))
      }
    }
  }
docs: 创建一个函数, 调用次数超过 count 次之后执行回调并将所有结果记住后返回
  
  @param {Number} count 调用次数
  @param {Function} callback 完成回调
  @return {Object}