js实现观察者模式

var publisher = {
	subscribers: {
		any: [] // event type: subscribers
	},

	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);
				}
			}
		}

	}
};



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

	o.subscribers = {any: []};
}

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

makePublisher(paper);

var joe = {
	drinkCoffee: function (paper) {
		console.log('Just read ' + paper);
	},

	sundayPreNap: function (monthly) {
		console.log('About to fall asleep reading this ' + monthly);
	}
};

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

paper.daily();
paper.daily();
paper.daily();
paper.monthly();