Javascript調用函數的繼承

Question

不知何故，JS繼承並沒有得到我的頭。我現在嘗試了很多東西，出於某種原因，我無法將方法添加到繼承的對象。

看到我的嘗試，定義B.setC，然後以後不可用。任何提示？

歡呼 湯姆

A = function(value){ 
     this.aValue = value; 
} 


B = function(value){ 
    A.call(this, value); 
    this.bValue=value+value; 
} 

B.prototype = Object.create(A.prototype);//subclass extends superclass 


B.setC = function(value){ 
    this.c = value+value+value; 
    console.log("execution"); 
} 

B.prototype.setD = function(value){ 
    this.D = value+value+value+value; 
    console.log("execution"); 
} 





x = new B("ConstructorParam"); 
x.setC("methodParam");// gives that setC is not a function 
x.setD("methodParam");// works but I added setD to A not B 

Answer 1

的混亂似乎來自這個誤會;引用您的評論：

其實這不是一個錯字。我想將setC添加到B而不是A，如果我的理解是正確的，並且我在Chrome中看到了調試，那麼如果我使用B.prototype.setB，則將setB添加到B aka A的原型而不是B。或者我錯過了什麼？

這也是由在問題此評論顯示：

x.setD("methodParam");// works but I added setD to A not B 

B.prototype不A。 B.prototype是以A.prototype爲原型的對象。您正確地將setD添加到B.prototype;它不以任何方式添加到A或A.prototype。

如果你想使用setC和setD你表現的方式，你可以把它們無論是在B.prototype（所以他們對B實例訪問）或A.prototype（所以他們訪問對A或B實例） 。

如果我們改變B.setC =到B.prototype.setC =，使d小寫匹配c，添加一些失蹤var S，以及創建和調用方法時使用較短的值，我們得到這樣的：

var A = function(value){ 
    this.aValue = value; 
}; 

var B = function(value){ 
    A.call(this, value); 
    this.bValue = value + value; 
}; 

B.prototype = Object.create(A.prototype);//subclass extends superclass 

B.setC = function(value){ 
    this.c = value + value + value; 
    console.log("execution"); 
}; 

B.prototype.setD = function(value){ 
    this.d = value + value + value + value; 
    console.log("execution"); 
}; 

var x = new B("b"); 
x.setC("c"); 
x.setD("d"); 

剛過了代碼最後一行，這就是我們在內存（減去了一堆不必要的細節）：

 
     +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ 
     |                | 
     \ +−−−−−−−−−−−−−−−+            | 
A−−−−−−−−−>| function |            | 
      +−−−−−−−−−−−−−−−+        +−−−−−−−−−−−−−+ | 
      | prototype  |−−−−−−−−−−−−−−−−−−−−−−−−−−−−>| object | |  
      +−−−−−−−−−−−−−−−+       /+−−−−−−−−−−−−−+ |  
                 | | constructor |−+ 
                 | +−−−−−−−−−−−−−+ 
     +−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−+ | 
     |           | | 
     \ +−−−−−−−−−−−−−−−+       | | 
B−−−−−−−−−>| function |       | | 
      +−−−−−−−−−−−−−−−+ +−−−−−−−−−−−−−−−−−−+ | | 
      | prototype  |−−−>|  object  | | | 
      +−−−−−−−−−−−−−−−+/+−−−−−−−−−−−−−−−−−−+ | | 
           | | constructor  |−+ | 
           | | setC: (function) | | 
           | | setD: (function) | | 
           | | [[Prototype]] |−−−+ 
      +−−−−−−−−−−−−−−−+ | +−−−−−−−−−−−−−−−−−−+ 
x−−−−−−−−−>| object  | | 
      +−−−−−−−−−−−−−−−+ | 
      | aValue: "a" | | 
      | bValue: "aa" | | 
      | c: "ccc"  | | 
      | d: "dddd"  | | 
      | [[Prototype]] |−−+ 
      +−−−−−−−−−−−−−−−+ 

[[Prototype]]以上就是規範使用的日名e包含對其原型對象的引用的對象的「內部槽」。相比之下，prototype函數的屬性（例如A.prototype）只是函數的一個正常屬性，它指向的對象將使用new作爲其創建的新對象的[[Prototype]]，前提是您使用該函數的new。

---

只是爲了完整性，這裏是ES2015 +：

class A { 
    constructor(value) { 
     this.aValue = value; 
    } 
} 

class B extends A { 
    constructor(value) { 
     super(value); 
     this.bValue = value + value; 
    } 

    setC(value) { 
     this.c = value + value + value; 
     console.log("execution"); 
    } 

    setD(value) { 
     this.d = value + value + value + value; 
     console.log("execution"); 
    } 
} 

let x = new B("b"); 
x.setC("c"); 
x.setD("d");