How to save .xlsx data to file as a 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;}

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.

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 });