0003 - observer pattern by angular service

使用angularjs实现ob：

<!-- lang: js -->
define(['../services'], function(services) {
'use strict';

services.factory('ob', [function() {
    var exports,
        channels = {};

    exports = {
        subscribe : function(topic, callback) {
            if (!_.isArray(channels[topic])) {
                channels[topic] = [];
            }

            var handlers = channels[topic];
            handlers.push(callback);
        },
        unsubscribe : function(topic, callback) {
            if (_.isArray(channels[topic])) {
                var handlers = channels[topic];

                var index = _.indexOf(handlers, callback);
                if (index >= 0) {
                    handlers.splice(index, 1);
                }
            }
        },
        publish : function(topic, data) {
            var self = this;

            var handlers = channels[topic] || [];
            _.each(handlers, function(handler) {
                try {
                    handler.apply(self, [data]);
                } catch (ex) {
                    console.log(ex);
                }
            });
        }
    };

    return exports;
}]);

});