面向对象的JS(2) JavaScript对面向对象的支持
1 实例方法
实例方法是由实例对象访问的方法，实例对象由new操作符创建。实例成员通过this关键字、prototype、构造器闭包或者Object.defineProperty来创建

function Cat(name) {
    var voice = "Meow";
    this.name = name;
    this.say = function () {
        return voice;
    }
}
Cat.prototype.eat = function () {
    return "Eating";
}
var cat = new Cat("Fluffy");
Object.defineProperty(cat, "numLegs", {
    value: 4,
    writable: true,
    enumerable: true,
    configurable: tr
    ue
});
console.log(cat.name); // Fluffy
console.log(cat.numLegs); // 4
console.log(cat.say()); // Meow
console.log(cat.eat()); // Eating

2 静态方法
JavaScript中没有对静态成员的直接支持。构造函数可以用来创建静态成员，静态成员不能被"this"关键字访问。
公有静态成员例子：

function Factory() {}
// public static method
Factory.getType = function () {
    return "Object Factory";
};
// public static field
Factory.versionId = "F2.0";
Factory.prototype.test = function () {
    console.log(this.versionId); // undefined
    console.log(Factory.versionId); // F2.0
    console.log(Factory.getType()); // Object Factory
}
var factory = new Factory();
factory.test();

私有静态成员例子：

var Book = (function () {
    // private static field
    var numOfBooks = 0;
    // private static method
    function checkIsbn(isbn) {
        if (isbn.length != 10 && isbn.length != 13)
            throw new Error("isbn is not valid!");
    }

    function Book(isbn, title) {
        checkIsbn(isbn);
        this.isbn = isbn;
        this.title = title;
        numOfBooks++;
        this.getNumOfBooks = function () {
            return numOfBooks;
        }
    }
    return Book;
})();
var firstBook = new Book("0-943396-04-2", "First Title");
console.log(firstBook.title); // First Title
console.log(firstBook.getNumOfBooks()); // 1
var secondBook = new Book("0-85131-041-9", "Second Title");
console.log(firstBook.title); // First Title
console.log(secondBook.title); // Second Title
console.log(firstBook.getNumOfBooks()); // 2
console.log(secondBook.getNumOfBooks()); // 2

3 抽象类型：
JavaScript是一种弱类型的语言，所以定义变量时不需要指定具体的类型。这减少了像接口这样的抽象层次需要。但当我们需要继承的时候，我们可以将一些公共函数放入抽象类中。

(function () {
    var abstractCreateLock = false;
    // abstract type
    function BaseForm() {
        if (abstractCreateLock)
            throw new Error("Can’t instantiate BaseForm!");
    }
    BaseForm.prototype = {};
    BaseForm.prototype.post = function () {
        throw new Error("Not implemented!");
    }

    function GridForm() {}
    GridForm.prototype = new BaseForm();
    abstractCreateLock = true;
    GridForm.prototype.post = function () {
        // ...
        return "Grid is posted.";
    }
    window.BaseForm = BaseForm;
    window.GridForm = GridForm;
})();
var myGrid = new GridForm();
console.log(myGrid.post()); // Grid is posted.
var myForm = new BaseForm(); // Error: Can’t instantiate BaseForm!

4 接口
在JavaScript中无直接的接口或者虚类支持。但可以由类似下面的代码来模拟，只留一个方法签名检查。

var Interface = function (name, methods) {
    this.name = name;
    // copies array
    this.methods = methods.slice(0);
};
Interface.checkImplements = function (obj, interfaceObj) {
    for (var i = 0; i < interfaceObj.methods.length; i++) {
        var method = interfaceObj.methods[i];
        if (!obj[method] || typeof obj[method] !== "function")
            throw new Error("Interface not implemented! Interface: " + interfaceObj.name + "Method: " + method);
    }
};
var iMaterial = new Interface("IMaterial", ["getName", "getPrice"]);

function Product(name, price, type) {
    Interface.checkImplements(this, iMaterial);
    this.name = name;
    this.price = price;
    this.type = type;
}
Product.prototype.getName = function () {
    return this.name;
};
Product.prototype.getPrice = function () {
    return this.price;
};
var firstCar = new Product("Super Car X11", 20000, "C