Javascript继承 - instanceof不工作？ [英] Javascript inheritance - instanceof not working?

问题描述

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;

I'm writing a simple platform game using javascript and html5. I'm using javascript in an OO manner. To get inheritance working i'm using the following;

// 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;

For the sake of this post consider the following example;

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!');

根据我的理解，我希望看到一个恐怖警报框，因为C是C& B& A的一个实例。我错了吗？或者我只是使用了错误的方法要检查？还是有copyPrototype诀窍t他是运营商吗？

As I understand it I would expect to see a horray alert box, because C is an instance of C & B & A. Am I wrong? Or am I just using the wrong method to check? Or has copyPrototype knackered the instanceof operator?

一如既往地感谢您花时间阅读本文！

Thanks as always for taking the time to read this!

Shaw。

推荐答案

这些天你不应该需要.prototype = new Thing（），我想我迟到了，但你可以在父节点的原型上使用Object.create，然后覆盖您感兴趣的方法覆盖。例如：

These days you shouldn't need .prototype = new Thing(), I think I'm late to the party but you can just use Object.create on the prototype of the parent and then override the methods you're interested in overriding. An example:

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：

If you run this code in node you will get:

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。

No worry about parameters to constructors or any such craziness.

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