Javascript - 如果超类构造函数接受参数，如何初始化超类 [英] Javascript - how to initialize super class if super class constructor takes arguments

问题描述

考虑以下Javascript代码段，

  var SuperClass = function（x）{
 this.x = x ; 
 this.a = 5; 
}; 
 
 var SubClass = function（x）{
} 
 
 function IntermediateClass（）{}; 
 IntermediateClass.prototype = SuperClass.prototype; 
 SubClass.prototype = new IntermediateClass; 
 SubClass.prototype.constructor = SubClass; 
  

现在如果我创建一个SubClass实例，该对象将不会初始化属性a和 x。

  var object = new SubClass; 
 //object.a == undefined 
 //object.x == undefined 
  

虽然我理解为什么会发生这种情况，但子类执行超类构造函数初始化的最简洁方法是什么？

解决方案

首先，该代码中存在大量错误。

这将使IntermediateClass成为SuperClass的姐妹。

  IntermediateClass.prototype = SuperClass.prototype; 
  

你永远不需要这样做，构造函数为你处理。

  SubClass.prototype.constructor = SubClass; 
  

也就是说，JavaScript 没有类。继承是基于对象的。你无法做你想要做的事情。

相反，我会在一个单独的函数中提取初始化，然后从子类中调用它。 / p>

一个更好的问题是你想要完成的事情。您正在尝试编写JavaScript，就好像它是Java一样。不是。

Consider the following Javascript snippet,

var SuperClass = function(x){
    this.x = x;
    this.a = 5;
};

var SubClass = function(x){
}

function IntermediateClass(){};
IntermediateClass.prototype = SuperClass.prototype;
SubClass.prototype = new IntermediateClass;
SubClass.prototype.constructor = SubClass;

Now If i create an instance of SubClass, the object will not initialize the property "a" and "x".

var object = new SubClass;
//object.a == undefined
//object.x == undefined

While I understand why this happens, what is the cleanest way for the subclass to perform the initialization done by the super class constructor?

解决方案

First of all, there's a bunch of errors in that code.

This will make IntermediateClass a sister of SuperClass.

IntermediateClass.prototype = SuperClass.prototype;

You never need to do this, constructor is handled for you.

SubClass.prototype.constructor = SubClass;

That said, JavaScript doesn't have classes. Inheritance is object-based. You can't do what you're trying to do.

Instead, I would extract the initialisation in a separate function, then call it from the "subclass".

A better question is what you're trying to accomplish. You're trying to write JavaScript as if it was Java. It's not.

这篇关于Javascript - 如果超类构造函数接受参数，如何初始化超类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！