axios 如何获取下载文件的进度条

exportFun(){

        let _that = this

        const instance = this.axios.create({

          onDownloadProgress: function(ProgressEvent) {

            const load = ProgressEvent.loaded;

            const total = ProgressEvent.total;

            const progress = (load / total) * 100;

            console.log(progress);

            bar.style.width=(progress) + "%";

            $("#total").html( Math.floor(progress) + "%")

            if(progress == 100){

              _that.$emit('exportDataFun',this.needData)

              _that.isDownLoad = false

            }

          } 

        });

        let ajaxUrl,fileName

        if(this.isCanClick){

          let _that =this

          _that.isCanClick = false

          instance({

            url: ajaxUrl,

            method: "post",

            data: this.needData,

            responseType: "blob" //application/octet-stream

          }).then(res => {

            const data = res.data

              let r = new FileReader()

              r.onload = function () {

                try {

                  let resData = JSON.parse(this.result)

                  console.log(resData)

                  if (resData && resData['code'] && resData['code'] != '1000') {

                    _that.$Message.info(resData.msg);

                    _that.isDownLoad = false

                  }

                } catch (err) {

                  // 兼容ie11

                  if (window.navigator.msSaveOrOpenBlob) {

                    try {

                      const blobObject = new Blob([data])

                      window.navigator.msSaveOrOpenBlob(blobObject, fileName)

                    } catch (e) {

                      console.log(e)

                    }

                    return

                  }

                  this.download(data, fileName)

                  alert('导出成功')

                }

              }

              r.readAsText(data) // FileReader的API

          }).catch(e => {

            let msg = "网络异常";

            alert(msg);

          });