文件下载通用方法

 /**
     * 文件下载
     */
    downloadFile(res) {
      const filename = res.headers["content-disposition"];
      const blob = new Blob([res.data]);

      var downloadElement = document.createElement("a");
      var href = window.URL.createObjectURL(blob);
      downloadElement.href = href;
      let downloadname = decodeURIComponent(filename.split("filename=")[1]);
      // downloadname = downloadname.replaceAll("\"", "");
      downloadname = downloadname.split('"').join("");
      downloadElement.download = downloadname;
      document.body.appendChild(downloadElement);
      downloadElement.click();
      document.body.removeChild(downloadElement);
      window.URL.revokeObjectURL(href);
    },