Lang: JavaScript

Javascript.FormatNumberWithCommas.js

var FormatNumberWithCommas = function(x) {
	return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
};

console.log(FormatNumberWithCommas(123456789));

Javascript.GenerateUUID.js

var UUID = function() {
  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
    return v.toString(16);
  });
};

console.log(UUID());