小程序返回的时间戳转化成时间

{
    "msg": "操作成功",
    "code": "0000",
    "data": [
        {
            "taskId": 1,        
            "taskStartTime": 1602432000000,
            "taskEndTime": 1602518400000
        },
        {
            "taskId": 2,         
            "taskStartTime": 1602432000000,
            "taskEndTime": 1602518400000
        }
    ]
}

<view class="cu-item" wx:for="{{timeList}}" wx:key="index"> 
    <view class=" text-left" >周期：{{item.taskStartTime}}~{{item.taskEndTime}}</view>
</view>

Page({
  data: {
    timeList: []
  },
  onLoad: function (options) {
    wx.request({
      url: 'http://www.xxxxx.com/1.json',
      header: {
        'content-type': 'application/json'
      },
      success: res => {
        this.setData({
          timeList: (res.data.data || []).map(a => {
            a.taskStartTime = typeof a.taskStartTime === 'number' ? this.formatDate(new Date(a.taskStartTime)) : a.taskStartTime.slice(0, 10)
            a.taskEndTime = typeof a.taskEndTime === 'number' ? this.formatDate(new Date(a.taskEndTime)) : a.taskEndTime.slice(0, 10)         
            return a
          })
        })
      }
    })
  },
  formatDate(date) {
    return date.getFullYear() + (date.getMonth() < 9 ? "-0" + (date.getMonth() + 1) : "-" + (date.getMonth() + 1)) + (date.getDate() < 10 ? "-0" + date.getDate() : "-" + date.getDate());
  },
})