javascript设计模式 – 单例模式原理与应用实例分

//懒汉模式单例demo
//懒汉模式只有在我需要实例的时候才会第一次实例化，只有当我第一次调用getInstance时才会去执行init获取实例。
var Singleton = (function () {
  var instantiated; 
  function init(){
    return {
      sayHello: function () {
        console.log('hello');
      }
    };
  }
 
  return {
    getInstance: function () {
      if(!instantiated){
        instantiated = init();
      }
      return instantiated;
    } 
  }
})();
 
//只能通过getInstance方法获取对象实例
var instance = Singleton.getInstance();
var instance2 = Singleton.getInstance();
instance.sayHello(); //hello
instance2.sayHello(); //hello
console.log(instance === instance2); //true
 
//饿汉模式demo
//饿汉模式在类初始化时就立刻执行getInstance进行赋值。
var Singleton = (function () {
  var instantiated = init();  //初始化时即对instantiated进行赋值
  function init(){
    return {
      sayHello: function () {
 console.log('hello');
   }
 };
  }
 
  return {
 getInstance: function () {
   return instantiated;
 } 
  }
})();
 
var instance = Singleton.getInstance();
var instance2 = Singleton.getInstance();
instance.sayHello(); //hello
instance2.sayHello(); //hello
console.log(instance === instance2); //true