listen on Model bound by popup

'popupVisible':{
          handler(val){
            if(val){
              setTimeout(() => {//
                this.$set(this.myAddressSlots[0],'defaultIndex',0);
              }, 100);
            }else{
              this.$set(this.myAddressSlots[0],'defaultIndex',1);
            }
          }
      }

roughly means: initialize the first item when it pops up. As for why the drop is set to 1 (1 is set at random), the purpose is that the defaultIndex will be different when it pops up again, and the defaultIndex will be different to initialize