观察者模式js实现

参看书籍JavaScript模式第七章设计模式
我的理解：观察者模式又叫订阅／发布模式。被观察者（发布者）内部需要有一些东西来处理观察者（订阅者）的方法。
发布者对象paper 需要有以下这些成员：
1、subscribers：
    一个数组
//存储每个事件类型下的订阅者。每个类型下订阅者是一个数组。
2、subscribe()：
    将订阅者添加到subscribers数组
//订阅者订阅某个类型，传入对应的回调函数。
3、unsubscribe()：
    从订阅者数组subscribers删除订阅者。
4、publish():
    循环遍历subscribers中的每个元素，并且调用他们注册时所提供的方法。
5、visitSubscribers()
    遍历操作订阅对象的方法。帮助方法。
如下：
发布者；

var publisher = {
    subscribers: {
        any: []           //事件类型：订阅者
    },
    subscribe: function(fn, type){
        type = type || "any";
        if (typeof this.subscribers[type] === "undefined"){
            this.subscribers[type] = []
        };
        this.subscribers[type].push(fn);
    },
    unsubscribe: function(fn,type){
        this.visitSubscribers('unsubscribe',fn,type);

    },
    publish: function(publication, type){
        this.visitSubscribers('publish',publication,type);

    },
    visitSubscribers: function (action, arg, type){
        var pubtype = type || 'any',
            subscribers = this.subscribers[pubtype],
            i,
            max = subscribers.length;
        for(i = 0;i < max; i += 1){
            if(action === 'publish'){
                subscribers[i](arg);
            }else {
                if (subscribers[i] === arg){
                    subscribers.splice(i, 1);
                }
            }
        }

    }

}

创造一个发布者；

function makePublisher(o){
    var i ;
    for (i in publisher){
        if(publisher.hasOwnProperty(i) && typeof publisher[i] === "function"){
            o[i] = publisher[i];
        }
    }
    o.subscribers = {
        any:[]
    }

}

发布者对象

var paper = {
    daily:function(){
        this.publish("bing news today");
    },
    monthly: function(){
        this.publish("interesting analysis", "monthly");
    },
    aha: function(){
        this.publish("aha","monday");
    }
};
makePublisher(paper);

订阅者对象

var joe = {
    drinkCoffee: function (paper){
        console.log("Just read" + paper);
    },
    sundayPreNap: function (monthly){
        console.log('About to fall asleep reading this'+ monthly);
    }
};

发布事件 和结果

paper.subscribe(joe.drinkCoffee);
paper.subscribe(joe.sundayPreNap, 'monthly');
paper.subscribe(joe.sundayPreNap, 'monday');


paper.daily();//Just readbing news today
paper.daily();//Just readbing news today
paper.daily();//Just readbing news today
paper.monthly();//About to fall asleep reading thisinteresting analysis
paper.aha();//About to fall asleep reading thisaha