calendar.js

var t = new Date();
var count = new Date(t.getFullYear(), t.getMonth() + 1, 0).getDate();
var offset = new Date(t.getFullYear(), t.getMonth(), 1).getDay();
var body = "";
for (var i = 0; i < offset; i++) {
    body += "   ";
}
for (var i = 1; i <= count; i++) {
    body += (" " + i).slice(-2);
    body += ((i + offset) % 7 == 0) ? "\n" : " ";
}
console.log(body);