How to dowload an excel file from backend in frontend?

I want to launch a browser download of an excel file generated in my backend, but I can't figure how to pass that kind of response.

app.get('/all', function (req, res) {
    db.query(...) LIMIT 20000;")
    .then(function (data) {
        let result = []
        data.forEach(element => {
            result.push(element)
        })

        /* make the worksheet */
        var ws = XLSX.utils.json_to_sheet(data);

        /* add to workbook */
        var wb = XLSX.utils.book_new();
        XLSX.utils.book_append_sheet(wb, ws, "All");

        XLSX.writeFile(wb, 'alltest1.xlsx'); //This saves the file in my server but I don't know how to send it as a response.

        console.log('Ready');

        res.send(result);
    })
    .catch(function (error) {
        console.log("ERROR:", error)
    })
})

I have been trying to create the excel in the frontend but chrome runs out of memory due to the big amount of data I think. I have also try to pass a buffer but the file I was getting seems to be corrupted.

Set the response header Content-Disposition and Content-Type of the file which tells the browser that file is send as response

res.setHeader('Content-Disposition',
        "attachment; filename='alltest1'; filename*=UTF-8\'\'alltest1.xlsx");
res.setHeader('Content-Type', "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");

and send the file content as response

res.send(wb)

OR you can also use res.download.

res.download(filePath, fileName, (err) => { if (err) console.log(err); })