如何在JavaScript中继承父对象的属性 [英] How to inherit properties from parent object in JavaScript

问题描述

我正在尝试创建一些对象和包装类来简化一些表单检查方法。我已经研究了JavaScript继承的标准例程，但是在运行代码时我遇到了一个相当奇怪的错误。以下是要点：

 功能 FooParent（a）{
  this  .prop = a; 
 此 .val = a.value;  //   *  
} 
  var  elem =  new  FooParent（  document  .getElementById（  someDomElement） ; 
 alert（elem.val）; 
  //  警告表单元素的值no概率！ 

如果我然后将此块添加到相同的代码：

  function  FooKid（a，b）{
 FooParent.call（ this ，b）; 
  this  .kidProp = b; 
} 
 FooKid.prototype =  new  FooParent （）; 
 FooKid.prototype。构造函数 = FooKid; 
  var  elem2 =  new  FooKid（ document  .getElementById（  someDomElement）; 
 alert（elem2.val）; 
  //  最后两行中的变量声明是无关紧要的，当我运行时代码在第3行中断在添加最后一个块之后。  

firebug给我的错误是在父对象中 this.val = a.value; 现在在尝试从它继承之前工作时是未定义的。我也试过...... this.val = this.prop.value ，和 this.val = prop.value （所有都应该指向相同的事情所以最后，我的问题是：为什么这个代码会破坏？bug在哪里？

解决方案

javascript继承：

  if （ typeof  Object.create！= = '  function'）{
 Object.create =  function （o）{
  function  F（）{} 
 F.prototype = o; 
 < span class =code-keyword> return   new  F（）; 
}; 
} 
 
  var  newObject1 = Object.create（{key1：'  valuekke'}）; 
  var  newObject2 = Object.create（newObje ct1）; 

在你的代码中，FooParent期待一个参数''a''

在你的行中...

  new  FooParent（）; 

...你还没有提供这个参数

I am trying to create some objects and wrapper classes to simplify some form checking methods. I have researched the standard routine for JavaScript inheritance but I am getting a rather odd error when running my code. Here is the gist:

function FooParent (a){
    this.prop = a;
    this.val = a.value;//*
}
var elem = new FooParent(document.getElementById("someDomElement");
alert(elem.val);
//alerts the value of the form element no prob!

If I then add this block to the same code:

function FooKid (a, b) {
    FooParent.call(this, b);
    this.kidProp = b;
}
FooKid.prototype = new FooParent();
FooKid.prototype.constructor = FooKid;
var elem2 = new FooKid(document.getElementById("someDomElement");
alert(elem2.val);
//the variable declaration in the last two lines is inconsequential, the code breaks on line 3 when I run it after adding the last block. 

The error that firebug gives me is that in the parent object this.val = a.value; is now undefined when it worked prior to trying to inherit from it. I also tried... this.val = this.prop.value, and this.val = prop.value (all should point to the same thing So in conclusion, my question is: why is this code breaking? Where is the bug?

解决方案

inheritance in javascript:

if (typeof Object.create !== 'function') {
	Object.create = function (o) {
		function F() { }
		F.prototype = o;
		return new F();
	};
}

var newObject1 = Object.create({key1:'valuekke'});
var newObject2 = Object.create(newObject1);

In you code FooParent expects a param ''a''
In your line...

new FooParent();

...you haven''t provided this param.

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