get请求是H5代码。可能会出现跨域问题，让服务端解决跨域问题，还有很多浏览器不支持，目前只有少数的几个浏览器支持下载

downFile (info) {
      let url = info.downPath//文件下载地址
      var xhr = new XMLHttpRequest();
      xhr.open("get", url, true);
      xhr.responseType = "blob";
      xhr.onload = function () {
        let blob = xhr.response
        if (window.navigator.msSaveOrOpenBlob) {
          navigator.msSaveBlob(blob, info.fileName)
        } else {
          let link = document.createElement('a')
          let evt = document.createEvent('HTMLEvents')
          evt.initEvent('click', false, false)
          link.href = URL.createObjectURL(blob)
          link.download = info.fileName
          link.style.display = 'none'
          document.body.appendChild(link)
          link.click()
          window.URL.revokeObjectURL(link.href)
        }
      };
      xhr.send();
    },

post请求是web端的，后端接口地址返回来的是文件流，没办法只能用这种方式，测试通过没问题

downOut () {
      const env = process.env.VUE_APP_ENV
      let url = config.baseUrl[env] + "Device/ExportDevice"//接口请求地址
      const req = new XMLHttpRequest();
      let formData = JSON.stringify(this.selectedRowKeys);//post请求参数
      req.open('POST', url, true);
      req.responseType = 'blob';
      req.setRequestHeader('Content-Type', 'application/json');
      req.setRequestHeader('token', localStorage.getItem('sysToken'))//携带token参数
      req.onload = () => {
        const data = req.response;
        const blob = new Blob([data], { type: "application/octet-stream" });
        const blobUrl = window.URL.createObjectURL(blob);
        this.download(blobUrl);
      };
      req.send(formData);
    },
    download (blobUrl) {
      const a = document.createElement('a');
      a.style.display = 'none';
      a.download = '批量导出设备信息.xlsx'; //文件名
      a.href = blobUrl;
      document.body.appendChild(a)
      a.click()
      window.URL.revokeObjectURL(a.href)
    },