如何从子级调用父级方法 [英] How to call parent method from child

问题描述

当我尝试调用pranet方法时出现此错误:Uncaught TypeError: Cannot read property 'call' of undefined

I'm getting this error when I'm trying to call pranet method: Uncaught TypeError: Cannot read property 'call' of undefined

http://jsfiddle.net/5o7we3bd/

function Parent() {
   this.parentFunction = function(){
      console.log('parentFunction');
   }
}
Parent.prototype.constructor = Parent;

function Child() {
   Parent.call(this);
   this.parentFunction = function() {
      Parent.prototype.parentFunction.call(this);
      console.log('parentFunction from child');
   }
}
Child.prototype = Object.create(Parent.prototype);
Child.prototype.constructor = Child;

var child = new Child();
child.parentFunction();

推荐答案

您没有在父母"原型上放置"parentFunction".您的父代"构造函数为 instance 添加了"parentFunction"属性，但是在原型上该函数将不可见.

You're not putting a "parentFunction" on the "Parent" prototype. Your "Parent" constructor adds a "parentFunction" property to the instance, but that won't be visible as a function on the prototype.

在构造函数中，this表示由于通过new调用而创建的新实例.向实例添加方法是一件好事，但这与向构造函数原型添加方法完全不同.

In a constructor function, this refers to the new instance that's been created as a result of calling via new. Adding methods to an instance is a fine thing to do, but it's not at all the same as adding methods to the constructor prototype.

如果要访问由父代"构造函数添加的"parentFunction"，则可以保存引用:

If you want to access that "parentFunction" added by the "Parent" constructor, you can save a reference:

function Child() {
   Parent.call(this);
   var oldParentFunction = this.parentFunction;
   this.parentFunction = function() {
      oldParentFunction.call(this);
      console.log('parentFunction from child');
   }
}

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