JavaScript对象子类 [英] JavaScript object sub-class

问题描述

我想创建继承自超类A的子类B.
我的代码在这里：

I want to create sub-class B that inherits from super-class A. my code here:

function A(){
    this.x = 1;
}

B.prototype = new A;
function B(){
    A.call(this);
    this.y = 2;
}
b = new B;
Console.log(b.x + " " + b.y );

运行时，显示B未定义。

when run it,it show B is undefined.

推荐答案

在尝试访问其原型之前，必须先定义B构造函数：

You must define the B constructor function before trying to access its prototype:

function A(){
  this.x = 1;
}

function B(){
  A.call(this);
  this.y = 2;
}

B.prototype = new A;

b = new B;
console.log(b.x + " " + b.y );  // outputs "1 2"

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