面向对象的程序设计（四）原型链继承

function SuperType() {
    this.property = true;
}

SuperType.prototype.getSuperValue = function () {
    return this.property;
}

function SubType() {
    this.subproperty = false;
}

//继承了SuperType
SubType.prototype = new SuperType();

SubType.prototype.getSubValue = function () {
    return this. subproperty;
}

var instance = new SubType();
alert(instance.getSuperValue());//true

alert(instance instanceof Object);//true
alert(instance instanceof SubType);//true
alert(instance instanceof SuperType);//true

alert(Object.prototype.isPrototypeOf(instance));//true
alert(SubType.prototype.isPrototypeOf(instance));//true
alert(SuperType.prototype.isPrototypeOf(instance));//true

//SubType继承了SuperType,通过创建SuperType的实例。
//弊端1：看下面的列子,instance3的colors属性居然被instance2改变了
//弊端2：没有办法在不影响所有对象实例的情况下，给超类型构造函数(SuperType2)传递参数
function SuperType2() {
    this.colors = ["red", "blue"];
}

function SubType2() {
}

SubType2.prototype = new SuperType2();

var instance2 = new SubType2();
instance2.colors.push("black");
alert(instance2.colors);//"red", "blue", "black"

var instance3 = new SubType2();
alert(instance3.colors);//"red", "blue", "black"