alpaca/src/js/Observable.js

Alpaca provides the easiest and fastest way to generate interactive forms for the web and mobile devices. It runs simply as HTML5 or more elaborately using Bootstrap, jQuery Mobile or jQuery UI. Alpaca uses Handlebars to process JSON schema and provide

(function($)
{
    var Alpaca = $.alpaca;

    Alpaca.Observable = Base.extend(
    {
        constructor: function(scope, id)
        {
            var _this = this;

            this.base();

            this.id = scope + "-" + id;

            this.value = null;
            this.subscribers = {};

            // array that contains observable whose value is dependent on our value
            this.dependentOnUs = {};


            // privileged functions

            this.notifySubscribers = function(prior)
            {
                var _this = this;

                $.each(this.subscribers, function(id, handler) {
                    handler(_this.value, prior);
                });
            };

            this.notifyDependents = function(prior)
            {
                $.each(this.dependentOnUs, function(key, observer) {
                    observer.onDependencyChange();
                });
            };

            // assume null value function
            this.valueFunction = null;
        },

        setValueFunction: function(valueFunction)
        {
            this.valueFunction = valueFunction;
            this.onDependencyChange();
        },

        /**
         * Registers a handler which acts as a subscriber.  When this observable value changes,
         * the handler method is raised.
         *
         * @param f
         */
        subscribe: function(id, handler)
        {
            if (!this.isSubscribed(id))
            {
                this.subscribers[id] = handler;
            }
        },

        unsubscribe: function(id)
        {
            delete this.subscribers[id];
        },

        isSubscribed: function(id)
        {
            return (this.subscribers[id] ? true: false);
        },

        markDependentOnUs: function(observable)
        {
            this.dependentOnUs[observable.id] = observable;
        },

        /**
         * Fired when one of our dependents has changed its value.
         */
        onDependencyChange: function()
        {
            var prior = this.get();

            // if we have a value calculation function, fire it
            if (this.valueFunction)
            {
                var current = this.valueFunction();

                // if the value changed, notify
                if (prior != current)
                {
                    this.set(current);
                }
            }
        },

        set: function(value)
        {
            var prior = this.value;
            this.value = value;

            // notify all dependents (observers that depend on our value)
            this.notifyDependents(prior);

            // notify all subscribers of the updated value
            this.notifySubscribers(prior);
        },

        get: function(_default)
        {
            var v = this.value;
            if (!v)
            {
                v = _default;
            }
            return v;
        },

        clear: function()
        {
            var prior = this.value;
            delete this.value;

            // notify all dependents (observers that depend on our value)
            this.notifyDependents(prior);

            // notify all subscribers of the updated value
            this.notifySubscribers(prior);
        }

    });

})(jQuery);