设置了responseType:Blob，通过 new FileReader() 解析blob为json，进行处理

 1         let that = this
 2         axios.get({
 3           url: ‘xxxxxx‘,
 4           method: ‘get‘,
 5           data:{},
 6           responseType: ‘blob‘, // 后台返回的数据会被强制转为blob类型
 7         }).then(res => {
 8           let reader = new FileReader();
 9           reader.readAsText(res)
10           reader.onload = function (result) {
11             try {
12               let resData = JSON.parse(result.target.result);  // 解析对象成功，说明是json数据
13               if (resData.code) {
14                 that.$message({
15                   type: ‘error‘,
16                   message: resData.desc
17                 })
18               }
19             } catch (err) {   // 解析成对象失败，说明是正常的文件流
20               let blob = new Blob([res], {type: "application/vnd.ms-excel"});
21               var link = document.createElement(‘a‘);
22               link.href = window.URL.createObjectURL(blob);
23               link.download = `文件名.xls`;
24               link.click()
25             }
26           };
27         })