Javascript ~ convert number display format

var num = 12345678;
var str = num + ""; // cast to string
var out = [];
for (var i = str.length - 3; i > 0; i -= 3) {
out.unshift(str.substr(i, 3));
}
out.unshift(str.substr(0, 3 + i));
out = out.join(','); // "12,345,678"


reference
http://stackoverflow.com/questions/1943828/convert-digital-display-format