5）Javascript设计模式：extends模式

简单的方式

function Person() {
    this.name = 'person';
}
Person.prototype.say = function() {};

function Child() {
    this.name = 'child';
}
Child.prototype = new Person();
 
var child = new Child();

缺点：其实child并不需要person里面的name属性

借用构造函数

function Person() {
    this.name = 'person';
}
Person.prototype.say = function() {};

function Child() {
     Person.call(this, arguments)
}

var child = new Child();

缺点：仅会复制父类对象的属性作为子类自身的属性, 仅仅是复制**

优点：可以获得父对象自身的真实副本，子类和父类没有关系，不会影响到父类**

借用构造函数是实现多继承

function CatWings() {
     Cat.call(this, arguments)
     Brid.call(this, arguments)
}

借用构造函数和实现原型

function Person() {
    this.name = 'person';
}
Person.prototype.say = function() {};

function Child() {
     Person.call(this, arguments)
    // this.name = 'child'
}

Child.prototype = new Person()

var child = new Child();
delete child.name;
// 可以看到访问：child.name的是prototype的

name属性被继承了2次

缺点：所有从Person继承的类，都是可以更改到Person的原型方法

临时构造函数

function inherit(Child, Parent) {
    var F = function(){}
    F.prototype = Parent.prototype;
    Child.prototype = new F();
    // Child.prototype.constructor = Child
    // Child.superclass = Parent.prototype;
}

// 每次都要创建一个空的F
var inherit = (function(){
    var F = Function(){};
    return function() {
        F.prototype = Parent.prototype;
        Child.prototype = new F();
        // Child.prototype.constructor = Child
        // Child.superclass = Parent.prototype;
    }
})();

Klass

var Klass = function (Parent, props) {

    if(props == undefined && typeof Parent == 'object') {
        props = Parent;
        Parent = null;
    }

    Parent = Parent || {};
    props = props || {};

    var Child = function() {
        if(Child.superclass.hasOwnProperty('__construct')) {
            Child.superclass['__construct'].apply(this, arguments);
        }

        if(Child.prototype.hasOwnProperty('__construct')) {
            Child.prototype['__construct'].apply(this, arguments);
        }
    };


    var F = function() {};
    F.prototype = Parent.prototype;
    Child.prototype = new F();
    Child.prototype.constructor = Child;
    Child.superclass = Parent.prototype;

    for(var i in props) {
        if(props.hasOwnProperty(i)) {
            Child.prototype[i] = props[i];
        }
    }
    return Child;
}

function Animal() {}

Animal.prototype.__construct = function(name) {
    this.name = name
};

Animal.prototype.getName = function() {
    return this.name;
};

var Dog = Klass(Animal, {
    __construct: function(name, age) {
        this.age = age;
    },
    run: function() {
        console.log('My name is %s, I\'m %s years old ,  I\'m Running', this.getName(), this.age);
    }
});

var dog = new Dog('xixi', 26)