return to give you an example, the arrow function is followed by return

Promise.resolve(1).then(v=> {
    console.log(v)//1
    return 123;
}).then(v => {
    console.log(v)//123
})

doctorComments(this.$route.params.hid, this.$route.params.fid, this.doctorHisId, this.createdon, this.pageno, 5)  //1.axios
.then(d => {//2.
  let dc = new Array()
  for(let i=0;i<d.list.length;iPP){
    dc[i] = {doctorComments:d.list[i],isZhanshiComment:false}
  }
  this.doctorComments = this.doctorComments.concat(dc);
  this.$refs.scroller.donePullup();
  return this.doctorComments;
})
.then((v)=>{//3. 
    console.log(v);vthis.doctorComments
})

the cause was later found out. This points to a method that is not the current vue instance in the method called after then. If you use this, in the called method, you will never find the value. According to the usage of Li Shisheng, pass the current vue instance before promise.

let that = this;//promise 
...//
.then() //
.then(func(that){...}); //


//
func(that){
that.xxx   //vue
that.xxx
}

. In the end,
is strictly a matter of scope.