How to save .xlsx data to file as a blob

The answer above is correct. Please be sure that you have a string data in base64 in the data variable without any prefix or stuff like that just raw data.

Here's what I did on the server side (asp.net mvc core):

string path = Path.Combine(folder, fileName);
Byte[] bytes = System.IO.File.ReadAllBytes(path);
string base64 = Convert.ToBase64String(bytes);

On the client side, I did the following code:

const xhr = new XMLHttpRequest();

xhr.open("GET", url);
xhr.setRequestHeader("Content-Type", "text/plain");

xhr.onload = () => {
    var bin = atob(xhr.response);
    var ab = s2ab(bin); // from example above
    var blob = new Blob([ab], { type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;' });

    var link = document.createElement('a');
    link.href = window.URL.createObjectURL(blob);
    link.download = 'demo.xlsx';

    document.body.appendChild(link);

    link.click();

    document.body.removeChild(link);
};

xhr.send();

And it works perfectly for me.

I've found a solution worked for me:

const handleDownload = async () => {
   const req = await axios({
     method: "get",
     url: `/companies/${company.id}/data`,
     responseType: "blob",
   });
   var blob = new Blob([req.data], {
     type: req.headers["content-type"],
   });
   const link = document.createElement("a");
   link.href = window.URL.createObjectURL(blob);
   link.download = `report_${new Date().getTime()}.xlsx`;
   link.click();
 };

I just point a responseType: "blob"

I had the same problem as you. It turns out you need to convert the Excel data file to an ArrayBuffer.

var blob = new Blob([s2ab(atob(data))], {
    type: ''
});

href = URL.createObjectURL(blob);

The s2ab (string to array buffer) method (which I got from https://github.com/SheetJS/js-xlsx/blob/master/README.md) is:

function s2ab(s) {
  var buf = new ArrayBuffer(s.length);
  var view = new Uint8Array(buf);
  for (var i=0; i!=s.length; ++i) view[i] = s.charCodeAt(i) & 0xFF;
  return buf;
}

This works as of: v0.14.0 of https://github.com/SheetJS/js-xlsx

/* generate array buffer */
var wbout = XLSX.write(wb, {type:"array", bookType:'xlsx'});
/* create data URL */
var url = URL.createObjectURL(new Blob([wbout], {type: 'application/octet-stream'}));
/* trigger download with chrome API */
chrome.downloads.download({ url: url, filename: "testsheet.xlsx", saveAs: true });