JavaScript对象子类

Question

我想创建继承自超类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

在尝试访问其原型之前,必须定义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"

Answer 2

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

应该

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

Answer 3

Lynda.com建议您接下来将构造函数重新分配给B,如下所示.

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

B.prototype = new A;
B.prototype.constructor = B;