JavaScript演示下Singleton设计模式

单例模式的基本结构：

MyNamespace.Singleton = function() {
	return {};
}();

比如：

MyNamespace.Singleton = (function() {
	return 
    { 
    	// Public members.
		publicAttribute1: true,
		publicAttribute2: 10,
		publicMethod1: function() {
		...
		},
		publicMethod2: function(args) 
    	{
			...
		}
	};
})();

但是，上面的Singleton在代码一加载的时候就已经建立了，怎么延迟加载呢？采用下面这种模式：

MyNamespace.Singleton = (function() {
	function constructor() 
    { 
    	// All of the normal singleton code goes here.
		...
	}
	return 
    {
		getInstance: function() 
        {
			// Control code goes here.
		}
	}
})();

具体来说，把创建单例的代码放到constructor里，在首次调用的时候再实例化：

完整的代码如下：

MyNamespace.Singleton = (function() {
	var uniqueInstance; // Private attribute that holds the single instance.
	function constructor() 
    { 
    	// All of the normal singleton code goes here.
		...
	}
	return 
    {
		getInstance: function() 
        {
			if(!uniqueInstance) { 
            // Instantiate only if the instance doesn't exist.
    		uniqueInstance = constructor();
		}
		return uniqueInstance;
	}
}
})();