vue 倒計時在ie內核的瀏覽器上時間顯示為NAN是怎么回事。

其他瀏覽器上都可以正常顯示，只有ie內核的顯示NAN。
<template>

  <span>{{time}}</span>

</template>

<script>
export default{
data () {

   return {
       time : '',
       flag : false
   }

},
mounted () {

let time = setInterval(()=>{
  if(this.flag == true){
    clearInterval(time)
  }
  this.timeDown()
 },500)

},
props : {

   endTime : {
       type : String
   }

},
methods : {

   timeDown () {
       const endTime = new Date(this.endTime)
       const nowTime = new Date();
       let leftTime = parseInt((endTime.getTime()-nowTime.getTime())/1000)
       let d = parseInt(leftTime/(24*60*60))
       let h = this.formate(parseInt(leftTime/(60*60)%24))
       let m = this.formate(parseInt(leftTime/60%60))
       let s = this.formate(parseInt(leftTime%60))
       if(leftTime <= 0){
           this.flag = true
           this.$emit('timeend')
       }
       this.time = `$dnpldpx天${h}時${m}分${s}秒`
   },
   formate (time) {
       if(time>=10){
           return time
       }else{
           return `0${time}`
       }
   }

}
}
</script>

上面是處理時間的js

下面這是后臺返回的時間格式
"2018-08-08 09:13:14"