悟透JavaScript

// 根类object定义
function object() { }

// 判断对象是否属于某类型
object.prototype.isA = function (aType) {
    var self = this.Type;
    while (self) {
        if (self == aType) return true;
        self = self.Base;
    }
    return false;
}

object.prototype.base = function () {
    var Base = this.Type.Base;

    if (!Base.Base) {   //已经是顶级了
        Base.apply(this, arguments);    // 直接调用基类构造函数
    } else {
        this.base = MakeBase(Base);     // 覆写this.base
        Base.apply(this, arguments);    // 调用基类构造函数
        delete this.base;               // 删除覆写的base属性
    }

    function MakeBase(Type) {
        var Base = Type.Base;
        if (!Base.Base) return Base;
        return function () {
            this.base = MakeBase(Base);
            Base.apply(this, arguments);
        }
    }
}

// 定义类
function Class(){
    var aDefine = arguments[arguments.length - 1];
    if(!aDefine) return;
    
    var aBase = arguments.length > 1?arguments[0]:object; // 解析基类
    
    function prototype_(){}     // 构造prototype的临时函数，用于挂接原型链
    
    prototype_.prototype = aBase.prototype;
    
    var aPrototype = new prototype_();
    
    // 复制类定义到当前类的prototype
    for(var member in aDefine){
        if(member != "Create"){ // 构造函数不用复制
            aPrototype[member] = aDefine[member];
        }
    }

    if (aDefine.toString != Object.prototype.toString)
        aPrototype.toString = aDefine.toString;
    if (aDefine.toLocaleString != Object.prototype.toLocaleString)
        aPrototype.toLocaleString = aDefine.toLocaleString;
    if (aDefine.valueOf != Object.prototype.valueOf)
        aPrototype.valueOf = aDefine.valueOf;

    // 如果有构造函数
    var aType;
    if (aDefine.Create) {
        aType = aDefine.Create;
    } else {
        aType = function () {
            this.base.apply(this, arguments);   // 调用基类构造函数
        };
    }

    aType.prototype = aPrototype;
    aType.Base = aBase;         // 设置类型关系，便于追溯
    aType.prototype.Type = aType;    // 为此类对象扩展一个Type属性
    
    return aType;
}

// 使用示例
var Person = Class({
    Create: function (name, age) {
        this.base();    // 调用上层构造函数
        this.name = name;
        this.age = age;
    },
    SayHello: function () {
        alert("Hello, I'm " + this.name + ", age " + this.age +".");
    },
    toString: function () {
        return this.name;
    }
});

var Employee = Class(Person, {
    Create: function (name, age, salary) {
        this.base(name, age);
        this.salary = salary;
    },
    ShowMeTheMoney: function () {
        alert(this + ", $" + this.salary);
    }
});

var BillGates = new Person("Bill Gates", 53);
var SteveJobs = new Employee("Steve Jobs", 59, 123);
alert(BillGates);
BillGates.SayHello();
SteveJobs.SayHello();
SteveJobs.ShowMeTheMoney();

// 用BillGate的类型建littleBill
var littleBill = new BillGates.Type("Little Bill", 6);
littleBill.SayHello();

alert(BillGates.isA(Person));   // true
alert(BillGates.isA(Employee)); // false
alert(SteveJobs.isA(Person));  // true