Or - build on @Jamaica Geek's answer, using Express - to avoid saving and reading a file:
res.attachment('file.xls');
var header="Sl No"+"\t"+" Age"+"\t"+"Name"+"\n";
var row1 = [0,21,'BOB'].join('\t')
var row2 = [0,22,'bob'].join('\t');
var c = header + row1 + row2;
return res.send(c);