vue axios 下载文件 onDownloadProgres

this.$http({
        url: this.$http.adornUrl("/fixedAssets/exportData"),
        method: "get",
        responseType: "blob",
        params: this.$http.adornParams(this.ajaxSeachData),
        timeout:1000 * 30000,
        onDownloadProgress: (evt) => {
        
         // 有时候拿不到total值，这个值总是为0
        //只要设置后台的代码  response.setContentLengthLong(文件长度); 就可以了
          alert(evt.total);

          this.percentage = parseInt(
            (evt.loaded / evt.total) * 100
          );
          if(this.percentage==100){
            this.progressSuccess='success';
          }
        },
      }).then(({ data }) => {

        this.showDownload = false;
        this.downLoadDialogVisible=false;

        if (data.code == 500) {
          this.$message.error(data.msg);
        } else {
          const blob = new Blob([data], {
            type: "application/octet-stream; charset=utf-8",
          });
          //对于<a>标签，只有 Firefox 和 Chrome（内核） 支持 download 属性
          //IE10以上支持blob但是依然不支持download
          if ("download" in document.createElement("a")) {
            //支持a标签download的浏览器
            var fileName="IT固定资产"+this.getNowTimeStr()+".xls";
            const link = document.createElement("a"); //创建a标签
            link.download = fileName; //a标签添加属性
            link.style.display = "none";
            link.href = URL.createObjectURL(blob);
            document.body.appendChild(link);
            link.click(); //执行下载
            URL.revokeObjectURL(link.href); //释放url
            document.body.removeChild(link); //释放标签
          } else {
            //其他浏览器
            navigator.msSaveBlob(blob, fileName);
          }
        }
      });