擴展繼承原型方法在Javascript

Question

我有一些類，相關的「父子」（構造函數）：

// Abstract root SuperClass 

function SuperClass() { 
    this.CLASS_ID = "SUPER-CLASS"; 
    throw new Error('Failed to instantiate abstract class' + this.CLASS_ID); 
} 

SuperClass.prototype.sayHello = function() { 
    alert('Hello, world!'); 
}; 

// Absctract ClassA inherits from SuperClass 
// inherit() and extend() are generic functions from the David Flanagan`s 
// brilliand book "Definitive Guide" 

function ClassA() { 
    this.CLASS_ID = "CLASS-A"; 
    throw new Error('Failed to instantiate abstract class' + this.CLASS_ID); 
} 

ClassA.prototype = inherit(SuperClass.prototype); 

// Concrete ClassB inherits from ClassA 

function ClassB(initData) { 
    this.CLASS_ID = "CLASS-B"; 
} 

ClassB.prototype = inherit(ClassA.prototype); 

extend(ClassB.prototype, { 
    constructor: ClassB, 

    welcomeNewDay: function() { 
     this.sayHello(); 
     this.doSomethingElse(); 
    }, 

    doSomethingElse: function(){ 
     alert('Jumping'); 
    } 
}); 

var classB = new ClassB(); 
classB.welcomeNewDay(); 

我怎樣才能正確地擴展抽象ClassA的方法.sayHello()沒有超載呢？

I`ve試圖讓這種方式：

extend(ClassA.prototype, { 
    sayHello: function() { 
     this.__proto__.sayHello(); 
     this.sing(); 
    }, 

    sing: function() { 
     alert('Lalala'); 
    } 
}); 

的問題是，.sing()被調用3次而不是1

如果我嘗試：

this.__proto__.sayHello.call(this); 

它拋出異常：

Uncaught RangeError: Maximum call stack size exceeded

Answer 1

嘗試訪問初始類：

extend(ClassA.prototype, { 
    sayHello: function() { 
     SuperClass.prototype.sayHello.call(this); 
     this.sing(); 
    }, 

    sing: function() { 
     alert('Lalala'); 
    } 
}); 

或只是存儲當前sayHello()方法：

var initialSayHello = ClassA.prototype.sayHello; 
extend(ClassA.prototype, { 
    sayHello: function() { 
     initialSayHello.call(this); 
     this.sing(); 
    }, 

    sing: function() { 
     alert('Lalala'); 
    } 
}); 

你需要有參照原sayHello()方法。

---

Uncaught RangeError: Maximum call stack size exceeded

它被拋出，因爲你確實有一個無限遞歸調用該方法的方法本身。