JavaScript 对象子类

Question

我想创建继承自父类(super class) A 的子类 B。我的代码在这里:

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。

Answer 1

您必须在尝试访问其原型(prototype)之前定义 B 构造函数:

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"