define(function () {    /**     * Event listener (singleton)     */    // TODO: replace usage of the event listener for the EventBus    var events = {        ‘listeners‘: [],        /**         * Find a single listener by its object         * @param {Object} object         * @return {Number} index  -1 when not found         */        ‘indexOf‘: function (object) {            var listeners = this.listeners;            for (var i = 0, iMax = this.listeners.length; i < iMax; i++) {                var listener = listeners[i];                if (listener && listener.object == object) {                    return i;                }            }            return -1;        },        /**         * Add an event listener         * @param {Object} object         * @param {String} event       The name of an event, for example ‘select‘         * @param {function} callback  The callback method, called when the         *                             event takes place         */        ‘addListener‘: function (object, event, callback) {            var index = this.indexOf(object);            var listener = this.listeners[index];            if (!listener) {                listener = {                    ‘object‘: object,                    ‘events‘: {}                };                this.listeners.push(listener);            }            var callbacks = listener.events[event];            if (!callbacks) {                callbacks = [];                listener.events[event] = callbacks;            }            // add the callback if it does not yet exist            if (callbacks.indexOf(callback) == -1) {                callbacks.push(callback);            }        },        /**         * Remove an event listener         * @param {Object} object         * @param {String} event       The name of an event, for example ‘select‘         * @param {function} callback  The registered callback method         */        ‘removeListener‘: function (object, event, callback) {            var index = this.indexOf(object);            var listener = this.listeners[index];            if (listener) {                var callbacks = listener.events[event];                if (callbacks) {                    index = callbacks.indexOf(callback);                    if (index != -1) {                        callbacks.splice(index, 1);                    }                    // remove the array when empty                    if (callbacks.length == 0) {                        delete listener.events[event];                    }                }                // count the number of registered events. remove listener when empty                var count = 0;                var events = listener.events;                for (var e in events) {                    if (events.hasOwnProperty(e)) {                        count++;                    }                }                if (count == 0) {                    delete this.listeners[index];                }            }        },        /**         * Remove all registered event listeners         */        ‘removeAllListeners‘: function () {            this.listeners = [];        },        /**         * Trigger an event. All registered event handlers will be called         * @param {Object} object         * @param {String} event         * @param {Object} properties (optional)         */        ‘trigger‘: function (object, event, properties) {            var index = this.indexOf(object);            var listener = this.listeners[index];            if (listener) {                var callbacks = listener.events[event];                if (callbacks) {                    for (var i = 0, iMax = callbacks.length; i < iMax; i++) {                        callbacks[i](properties);                    }                }            }        }    };    return events;});