vue 在方法中循环复制,watch监听不到

最近在学习vue,遇到了这样一个问题.

this.bussno值的改变无法及时触发watch监听,只有在方法执行完,才会监听到最后一次值的改变,想不清楚是为什么.

赋值方法如下

for(let i=0;i<fileList.length;i++){
            this.flag =i;
            let saveData =new Object();
            let fileType = fileList[i].type;
            let arrayType = fileType.split("/");
            if(arrayType.length > 1 && arrayType[0] == "image") {
              saveData.imgfileflag = "1";
            }else {
              saveData.imgfileflag = "0";
            }
            let subStr =fileList[i].webkitRelativePath.split("/");
            //承保or理赔
            if(system =="Claim"){
              saveData.typepath = fileList[i].webkitRelativePath;
              this.bussno=subStr[2];
            }else if(system =="Prpall"){
              saveData.typepath= "";
              let index =fileList[i].name.indexOf(".");
              this.bussno=fileList[i].name.substring(0,index);
            }

watch监听

watch:{
        bussno:{
          handler(newVal,oldVal){
            console.log(newVal);
            //最大号,
            let that =this;
            that.bussnoList.push(newVal);
            if(that.system =="Claim"){
              getAction(that.url.maxNo,{systemCode:that.system,bussNo:newVal}).then(res=>{
                debugger;
                if(res.success){
                  that.maxNo=res.result;
                }else{
                  that.$message.error(res.message)
                }
              });
            }
          }
        },
        immediate: true,
      },

求大佬解答!

https://www.jb51.net/article/147185.htm

vue采用微任务队列去轮询watcher，连续的两次改变是同步的，所以回调队列中只会添加一次回调
https://segmentfault.com/q/1010000039288976