单例

var mySingleton = (function(){
var instance;
function init(){
var privateRandomNumber = Math.random();
return{
getRandomNumber:function(){
return privateRandomNumber;
}
}
};
return {
getInstance :function(){
if(!instance){
instance = init();
}
return instance;
}
};

})();
var SA = mySingleton.getInstance();
var SB = mySingleton.getInstance();
alert(SA.getRandomNumber() === SB.getRandomNumber());