几种用JavaScript实现的单例模式(Singleton Design Pattern)

</div><div>var Singleton = function() {  </div><div> var attr = 1, fn = function(){ console.log("I am executed in closure");};  </div><div> return {  </div><div>   method : function(){ fn(); },  </div><div>   getAttr : function(){ console.log("will be returned: " + attr ); return attr; }  </div><div> };  </div><div>}();  </div><div>Singleton.method();  </div><div>Singleton.getAttr();  </div><div>var LazySingleton = function(){  </div><div>var attr = 2, fn = function(){ console.log("I am LazySingleton function");};  </div><div>var obj = {  </div><div>method : function(){ fn(); },  </div><div>getAttr : function(){ return attr; }  </div><div>};  </div><div>function init(){  </div><div>return obj;  </div><div>}  </div><div>return { getInstance: init};  </div><div>}();  </div><div>LazySingleton.getInstance().method();  </div><div>console.log("LazySingleton: " + LazySingleton.getInstance().getAttr());  </div><div>function Universe() {</div><div>    if (typeof Universe.instance === 'object') {</div><div>        return Universe.instance;</div><div>    }</div><div>    this.start_time = 0;</div><div>    this.bang = "Big";</div><div>    Universe.instance = this;</div><div>    // return this implicitly</div><div>}</div><div>// test</div><div>var uni = new Universe();</div><div>var uni2 = new Universe();</div><div>console.log(uni === uni2); // true</div><div>function Universe2() {</div><div>    // instance cached</div><div>    var instance = this;</div><div>    this.start_time = 0;</div><div>    this.bang = "Big";</div><div>    Universe2 = function () {</div><div>        return instance;</div><div>    };</div><div>}</div><div>var un1i = new Universe2();</div><div>var un1i2 = new Universe2();</div><div>un1i.bang = "123";</div><div>console.log(un1i === un1i2); // true</div><div>console.log(un1i2.bang); // 123</div><div>var Universe3;</div><div>(function () {</div><div>    var instance;</div><div>    Universe3 = function Universe3() {</div><div>        if (instance) {</div><div>            return instance;</div><div>        }</div><div>        instance = this;</div><div>        this.start_time = 0;</div><div>        this.bang = "Big";</div><div>    };</div><div>} ());</div><div>var a = new Universe3();</div><div>var b = new Universe3();</div><div>alert(a === b); // true</div><div>a.bang = "123";</div><div>alert(b.bang); // 123</div><div>