JavaScript Singleton with lazy instantiation.

lazySingleton.js

var ConstructorName = (function()
{
	var singletonInstance = null;
	
	function ConstructorName()
	{
		// presumably expensive instantiation/init code
	}

	return function ()
	{
		if (singletonInstance === null)
		{
			singletonInstance = new ConstructorName();
		}
		return singletonInstance;
	};
})();