javascript面向對象編程實現[定義（靜態）屬性方法--繼承]

        javascript面向對象編程實現:
            1.類的聲明:
                function test1(){
                    this.p1 = "p1";
                    this.p2 = "p2";
                    this.f1 = function(){ alert("f1"); }
                    this.f2 = function(){ akert("f2"); }
                }
                上面的代碼聲明瞭兩個公有的屬性p1和p2,兩個方法f1和f2.
                如何申明私有變量呢?
                function test1(){
                    var _test = "test";
                    this.p1 = "p1";
                    this.p2 = "p2";
                    this.f1 = function(){ alert("f1"); }
                    this.f2 = function(){ akert("f2"); }
                }
                上面的代碼通過var關鍵字聲明瞭一個局部變量_test,其作用域是test1類定義的內部,對外不公開.
                如何申明類的靜態變量和靜態方法呢?
                test1.staticProp = "static var";
                test1.staticMethod = function(){
                    alert("static method");
                }
                還可以通過javascript中對象的prototype屬性來申明類的實例屬性或方法:
                test1.prototype.prop2 = "prop2";
                test2.prototype.method2 = function(){
                    alert(" this.prop2");
                }
`               利用prototype屬性,可以實現另一種類的聲明方法:
                function test(){}
                test.prototype = {
                    p1 : "p1",
                    p2 : "p2",
                    f1 : function(){
                        alert("f1");
                    }
                  }
                
                如何實現類的繼承呢?通過複製父類的所有屬性和方法來實現子類的繼承:
                用for(....in ....)方法來實現遍歷父類所有的屬性和方法
                這裏看看我如何讓新聲明的test1類繼承test類的:
                function test1(){}//定義新聲明的test1類.
                var p;                
                for(p in test.prototype){    //遍歷父類的所有屬性和方法
                    test1.prototype[p] = test.prtotype[p];   //把父類的所有屬性和方法全部複製到新聲明的子類test1中
                }
                test1.prototype.newMethod = function(){//定義新聲明的子類test1的新方法
                    alert("new method");
                }
                其實prototype框架已經幫我們實現了這種繼承,我們來看看它是如何實現的:
                Object.extend = function(destination, source){
                    for(property in source){
                        destination[property] = source[property];
                    }
                    return destination;
                 }
                Prototype框架爲Object對象定義了extend方法,該方法有兩個參數destination和source,分別對應於子類和父類,所以我們前面所講的test1繼承test可以簡化代碼如下:
                 function test1(){
                    test1.prototype = Object.extend({
                        newMethod : function(){
                            alert("new method");
                        }
                    },
                    test.prototype
                );
            
                如果我們改變一下上述代碼中extend方法中的兩個參數的順序:
               function test1(){
                    test1.prototype = Object.extend(
                        test.prototype,
                        {
                        newMethod : function(){
                            alert("new method");
                        }
                    },
                );  
                   可以發現,對於test1子類來說效果是相同的..
                    但是,我們進一步會發現,父類test確擁有了子類test1的新增方法,雖然這不是我們最初想要的繼承效果,但是這種方法卻使我們有了擴展對象屬性或者方法的手段了,不是嗎?