So I am retrieving a file from backend. I want to convert the file back to .xlsx format from Base64 and download said file. However, after downloading the file and opening it, it gives the error "Excel cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file."

I am saving the file using filesaverjs.

The file is encoded like this:

data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,UEsDBBQABgAIA...

Here's my code:

function convertToFile(file){
    var arr = file.FILE_ENCODE.split(','),
    mime = arr[0].match(/:(.*?);/)[1],
    bstr = Buffer.from(arr[1]).toString('binary'),
    n = bstr.length,
    u8arr = new Uint8Array(n);
    while(n--){
    u8arr[n] = bstr.charCodeAt(n);
    }
    saveAs(new File([u8arr], "test.xlsx", {type:mime}))
}

Not sure exactly what I am doing wrong so any help would be immensely appreciated.