Javascript继承 - instanceof不工作？

Question

我正在使用javascript和html5编写一个简单的平台游戏.我正在以OO方式使用javascript.为了继承工作,我正在使用以下内容;

// http://www.sitepoint.com/blogs/2006/01/17/javascript-inheritance/
function copyPrototype(descendant, parent) {
    var sConstructor = parent.toString();
    var aMatch = sConstructor.match(/\s*function (.*)\(/);
    if (aMatch != null) { descendant.prototype[aMatch[1]] = parent; }
    for (var m in parent.prototype) {
        descendant.prototype[m] = parent.prototype[m];
    }
};

为了这篇文章,请考虑以下示例;

function A() {
 this.Name = 'Class A'
}
A.prototype.PrintName = function () {
 alert(this.Name);
}

function B() {
 this.A();
}
copyPrototype(B, A);

function C() {
 this.B();
}
copyPrototype(C, B);

var instC = new C();

if (instC instanceof A)
  alert ('horray!');

据我了解,我希望看到一个恐怖警报框,因为C是C&B&A的一个例子.我错了吗？或者我只是用错误的方法来检查？或者copyPrototype是否使用了instanceof运算符？

一如既往地感谢您花时间阅读本文!

肖.

Answer 1

问题是该copyPrototype函数只将属性从构造函数原型复制到另一个,例如,最后,简单指向的内部[[Prototype]]链接.C.prototypeObject.prototype

原型链instC和构造函数的原型看起来像这样:

                [[Prototype]]
    A.prototype -------------->|-------------------|
                               |                   |
    B.prototype -------------->|  Object.prototype | ---> null
                               |                   |
    C.prototype -------------->|-------------------|
        ^
        |
      instC

该instanceof运营商遍历原型链,你的instC目标,你可以看到,会对它的原型链只C.prototype和Object.prototype.

您可以通过将构造函数的原型设置为其"父"构造函数的对象实例来实现所需的功能,例如:

function A() {
  this.Name = 'Class A'
}

A.prototype.PrintName = function () {
  alert(this.Name);
}

function B() {
  //..
}
B.prototype = new A();
B.prototype.constructor = B; // fix constructor property


function C() {
  //..
}

C.prototype = new B();
C.prototype.constructor = C; // fix constructor property

var instC = new C();
if (instC instanceof A)
  alert('horray!');

现在instC对象的原型链看起来像这样:

           ---------------        ---------------        ---------------
 instC --> | C.prototype | -----> | B.prototype | -----> | A.prototype |
           ---------------        ---------------        ---------------
                                                                |
                                                                V
                                                       --------------------
                                                       | Object.prototype |
                                                       --------------------
                                                                |
                                                                V
                                                               null

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Answer 2

这些天你不应该需要.prototype = new Thing(),我想我迟到了,但是你可以在父节点的原型上使用Object.create,然后覆盖你感兴趣的方法覆盖.一个例子:

var IDataSource = function(){
    throw new Error("Not implemented, interface only");
};

IDataSource.prototype.getData = function(){
    throw new Error("Not implemented.");
};

var BasicDataSource = function(){};
BasicDataSource.prototype = Object.create(IDataSource.prototype);
BasicDataSource.prototype.getData = function(){
    //[do some stuff, get some real data, return it]
    return "bds data";
};

var MockDataSource = function(){};
MockDataSource.prototype = Object.create(IDataSource.prototype);
MockDataSource.prototype.getData = function(){
    //[DONT DO some stuff return mock json]
    return "mds data";
};

MockDataSource.prototype.getDataTwo = function(){
    //[DONT DO some stuff return mock json]
    return "mds data2";
};


var MockDataSource2 = function(){};
MockDataSource2.prototype = Object.create(MockDataSource.prototype);




var bds = new BasicDataSource();
console.log("bds is NOT MockDataSource:", bds instanceof MockDataSource);
console.log("bds is BasicDataSource:", bds instanceof BasicDataSource);
console.log("bds is an IDataSource:", bds instanceof IDataSource);
console.log("bds Data:", bds.getData());


var mds = new MockDataSource();
console.log("mds is MockDataSource:", mds instanceof MockDataSource);
console.log("mds is NOT a BasicDataSource:", mds instanceof BasicDataSource);
console.log("mds is an IDataSource:", mds instanceof IDataSource);
console.log("mds Data:", mds.getData());
console.log("mds Data2:",mds.getDataTwo());


var mds2 = new MockDataSource2();
console.log("mds2 is MockDataSource2:", mds2 instanceof MockDataSource2);
console.log("mds2 is MockDataSource:", mds2 instanceof MockDataSource);
console.log("mds2 is NOT a BasicDataSource:", mds2 instanceof BasicDataSource);
console.log("mds2 is an IDataSource:", mds2 instanceof IDataSource);
console.log("mds2 Data:", mds2.getData());
console.log("mds2 Data2:",mds2.getDataTwo());

如果您在节点中运行此代码,您将获得:

bds is NOT MockDataSource: false
bds is BasicDataSource: true
bds is an IDataSource: true
bds Data: bds data
mds is MockDataSource: true
mds is NOT a BasicDataSource: false
mds is an IDataSource: true
mds Data: mds data
mds Data2: mds data2
mds2 is MockDataSource2: true
mds2 is MockDataSource: true
mds2 is NOT a BasicDataSource: false
mds2 is an IDataSource: true
mds2 Data: mds data
mds2 Data2: mds data2

不用担心构造函数的参数或任何这样的疯狂.