js单例

var singleton = (function(){
function Singleton(args)
{
var args = args || {};
this.pointX = args.pointX || 10;
this.pointY = args.pointY || 15;
}
var instance;
var _static = {
getInstance : function(args){
if(instance===undefined)
instance = new Singleton(args);
return instance;
}
};
return _static;
})();
var single = singleton.getInstance({pointX:5});
var single2 = singleton.getInstance();
alert(single.pointX);
alert(single2.pointX);
alert(single === single2);