单例模式

一、实现单例模式

    var Singleton = function(name){
        this.name = name;
        this.instance = null;
    };

    Singleton.prototype.getName = function(){
        alert(this.name);
    };

    Singleton.getInstance = function(name){
        if(!this.instance){
            this.instance = new Singleton(name);
        }
        return this.instance;
    };
    var a = Singleton.getInstance('tiany1');
    var b = Singleton.getInstance('tiany2');

    alert(a===b);     //true

或者

var Singleton = function(name){
        this.name = name;
        this.instance = null;
    };

    Singleton.prototype.getName = function(){
        alert(this.name);
    };

    Singleton.getInstance = (function(name){
        var instance = null;
        return function(name){
            if(!instance) {
                instance = new Singleton(name);
            }
            return instance;
        }   
    })();

    var a = Singleton.getInstance('tiany1');
    var b = Singleton.getInstance('tiany2');

    alert(a===b);     //true

二、透明的单例模式

    var CreateDiv = (function(){
        var instance;

        var CreateDiv = function(html){
            if(instance){
                return instance;
            }
            this.html = html;
            this.init();
            return instance = this;
        };

        CreateDiv.prototype.init = function(){
                var div = document.createElement('div');
                div.innerHTML = this.html;
                document.body.appendChild(div);
        };

        return  CreateDiv;

    })();

    var a = new CreateDiv('tiany1');          //生成<div>tiany1</div>
    var b = new CreateDiv('tiany2');

    alert(a===b);   //true

三、用代理实现单例模式

          var CreateDiv = function(html){
            this.html = html;
            this.init();
        };

        CreateDiv.prototype.init = function(){
                var div = document.createElement('div');
                div.innerHTML = this.html;
                document.body.appendChild(div);
        };

        //接下来引入代理类 proxySingletonCreateDiv

        var proxySingletonCreateDiv = (function(){
            var instance;
            return function(html){
                if(!instance){
                    instance = new CreateDiv(html);
                }
                return instance;
            }
        })();
    
    var a = new proxySingletonCreateDiv('tiany1');        //生成<div>tiany1</div>
    var b = new proxySingletonCreateDiv('tiany2');

    alert(a===b);   //true

四、JavaScript中的单例模式

在JavaScript中创建对象的方法非常简单，既然我们只需要“唯一”的对象，那我们为它先创建一个“类”。
单例模型的核心是 ** 确保只有一个实例，并提供全局访问**
1、使用命名空间

var namespace1={
    a: function(){
         alert(1); 
    },
    b: function(){
         alert(1); 
    }
};

2、使用闭包封装私有变量

var user = (function(){
        var _name = 'tiany',
            _age = 28;

            return{
                getUserInfo : function(){
                    return  _name+"-"+_age;
                }
            }
    })();

五、惰性单例

惰性单例指的是在需要的时候才创建对象实例

var LazySingle = ( function () {
        // 单例引用
        var _instance = null;
        // 单例
        function Single() {
            return {
                // 这里定义私有属性和方法
                publicMethod : function () {},
                publicProperty : '1.0'
            }
        }
        // 获取单例接口
        return function () {
            // 如果为创建单例将创建单例
            if ( ! _instance ) {
                _instance = Single();
            } 
            // 返回单例
            return _instance;
        }
        
    } )();