JavaScript继承

//定义父类
function Parent(x, y){
	this.x = x;
	this.y = y;
}
//定义父类的实例方法
Parent.prototype.sum = function(){
    return this.x + this.y;	
}

//定义子类并继承Parent
function Child(x, y, z){
	// 据说下面这行可以用于单层的继承，但是我的浏览器中会报错：TypeError: this.superclass is not a function
	//this.superclass(x, y);
	//调用构造函数链
	//Parent.call(this, x, y);  
    this.z = z;	
}

//继承Parent的原型，如果没这句，则默认继承Object的原型
Child.prototype = new Parent();  
//不需要的属性删除
delete Child.prototype.x;
delete Child.prototype.y;

//前面我们用Parent创建了Child的原型对象，所以需要重新给原型对象的constructor属性赋值,否则该属性和Parent的constructor相同
Child.prototype.constructor = Child; 

Child.prototype.multiply = function(){
    return this.x * this.y * this.z;	
}

var parent = new Parent(1,2);
var child = new Child(1,2,3);
alert(parent.sum());  //ok
alert(child.sum());  //ok
alert(child.multiply());  //ok
alert(parent.multiply());  //error:no such method