API: event Event.js (YUI Library)

# Yahoo! UI Library

### Event Utility 2.2.2

Yahoo! UI Library > event > Event.js (source view)

    /**
     * The Event Utility provides utilities for managing DOM Events and tools
     * for building event systems
     *
     * @module event
     * @title Event Utility
     * @namespace YAHOO.util
     * @requires yahoo
     */

    // The first instance of Event will win if it is loaded more than once.
    // @TODO this needs to be changed so that only the state data that needs to
    // be preserved is kept, while methods are overwritten/added as needed.
    // This means that the module pattern can't be used.
    if (!YAHOO.util.Event) {

    /**
     * The event utility provides functions to add and remove event listeners,
     * event cleansing.  It also tries to automatically remove listeners it
     * registers during the unload event.
     *
     * @class Event
     * @static
     */
        YAHOO.util.Event = function() {

            /**
             * True after the onload event has fired
             * @property loadComplete
             * @type boolean
             * @static
             * @private
             */
            var loadComplete =  false;

            /**
             * True when the document is initially usable
             * @property DOMReady
             * @type boolean
             * @static
             * @private
             */
            var DOMReady = false;

            /**
             * Cache of wrapped listeners
             * @property listeners
             * @type array
             * @static
             * @private
             */
            var listeners = [];

            /**
             * User-defined unload function that will be fired before all events
             * are detached
             * @property unloadListeners
             * @type array
             * @static
             * @private
             */
            var unloadListeners = [];

            /**
             * Cache of DOM0 event handlers to work around issues with DOM2 events
             * in Safari
             * @property legacyEvents
             * @static
             * @private
             */
            var legacyEvents = [];

            /**
             * Listener stack for DOM0 events
             * @property legacyHandlers
             * @static
             * @private
             */
            var legacyHandlers = [];

            /**
             * The number of times to poll after window.onload.  This number is
             * increased if additional late-bound handlers are requested after
             * the page load.
             * @property retryCount
             * @static
             * @private
             */
            var retryCount = 0;

            /**
             * onAvailable listeners
             * @property onAvailStack
             * @static
             * @private
             */
            var onAvailStack = [];

            /**
             * Lookup table for legacy events
             * @property legacyMap
             * @static
             * @private
             */
            var legacyMap = [];

            /**
             * Counter for auto id generation
             * @property counter
             * @static
             * @private
             */
            var counter = 0;

            /**
             * addListener/removeListener can throw errors in unexpected scenarios.
             * These errors are suppressed, the method returns false, and this property
             * is set
             * @property lastError
             * @type Error
             */
            var lastError = null;

            return {

                /**
                 * The number of times we should look for elements that are not
                 * in the DOM at the time the event is requested after the document
                 * has been loaded.  The default is 200@amp;50 ms, so it will poll
                 * for 10 seconds or until all outstanding handlers are bound
                 * (whichever comes first).
                 * @property POLL_RETRYS
                 * @type int
                 * @static
                 * @final
                 */
                POLL_RETRYS: 200,

                /**
                 * The poll interval in milliseconds
                 * @property POLL_INTERVAL
                 * @type int
                 * @static
                 * @final
                 */
                POLL_INTERVAL: 10,

                /**
                 * Element to bind, int constant
                 * @property EL
                 * @type int
                 * @static
                 * @final
                 */
                EL: 0,

                /**
                 * Type of event, int constant
                 * @property TYPE
                 * @type int
                 * @static
                 * @final
                 */
                TYPE: 1,

                /**
                 * Function to execute, int constant
                 * @property FN
                 * @type int
                 * @static
                 * @final
                 */
                FN: 2,

                /**
                 * Function wrapped for scope correction and cleanup, int constant
                 * @property WFN
                 * @type int
                 * @static
                 * @final
                 */
                WFN: 3,

                /**
                 * Object passed in by the user that will be returned as a
                 * parameter to the callback, int constant
                 * @property OBJ
                 * @type int
                 * @static
                 * @final
                 */
                OBJ: 3,

                /**
                 * Adjusted scope, either the element we are registering the event
                 * on or the custom object passed in by the listener, int constant
                 * @property ADJ_SCOPE
                 * @type int
                 * @static
                 * @final
                 */
                ADJ_SCOPE: 4,

                /**
                 * Safari detection is necessary to work around the preventDefault
                 * bug that makes it so you can't cancel a href click from the
                 * handler.  Since this function has been used outside of this
                 * utility, it was changed to detect all KHTML browser to be more
                 * friendly towards the non-Safari browsers that share the engine.
                 * Internally, the preventDefault bug detection now uses the
                 * webkit property.
                 * @property isSafari
                 * @private
                 * @static
                 * @deprecated
                 */
                isSafari: (/KHTML/gi).test(navigator.userAgent),

                /**
                 * If WebKit is detected, we keep track of the version number of
                 * the engine.  The webkit property will contain a string with
                 * the webkit version number if webkit is detected, null
                 * otherwise.
                 * Safari 1.3.2 (312.6): 312.8.1 <-- currently the latest
                 *                       available on Mac OSX 10.3.
                 * Safari 2.0.2: 416 <-- hasOwnProperty introduced
                 * Safari 2.0.4: 418 <-- preventDefault fixed (I believe)
                 * Safari 2.0.4 (419.3): 418.9.1 <-- current release
                 *
                 * http://developer.apple.com/internet/safari/uamatrix.html
                 * @property webkit
                 * @type string
                 * @static
                 */
                webkit: function() {
                    var v=navigator.userAgent.match(/AppleWebKit\/([^ ]*)/);
                    if (v&&v[1]) {
                        return v[1];
                    }
                    return null;
                }(),

                /**
                 * IE detection needed to properly calculate pageX and pageY.
                 * capabilities checking didn't seem to work because another
                 * browser that does not provide the properties have the values
                 * calculated in a different manner than IE.
                 * @property isIE
                 * @private
                 * @static
                 */
                isIE: (!this.webkit && !navigator.userAgent.match(/opera/gi) &&
                        navigator.userAgent.match(/msie/gi)),

                /**
                 * poll handle
                 * @property _interval
                 * @private
                 */
                _interval: null,

                /**
                 * @method startInterval
                 * @static
                 * @private
                 */
                startInterval: function() {
                    if (!this._interval) {
                        var self = this;
                        var callback = function() { self._tryPreloadAttach(); };
                        this._interval = setInterval(callback, this.POLL_INTERVAL);
                    }
                },

                /**
                 * Executes the supplied callback when the item with the supplied
                 * id is found.  This is meant to be used to execute behavior as
                 * soon as possible as the page loads.  If you use this after the
                 * initial page load it will poll for a fixed time for the element.
                 * The number of times it will poll and the frequency are
                 * configurable.  By default it will poll for 10 seconds.
                 *
                 * @method onAvailable
                 *
                 * @param {string}   p_id the id of the element to look for.
                 * @param {function} p_fn what to execute when the element is found.
                 * @param {object}   p_obj an optional object to be passed back as
                 *                   a parameter to p_fn.
                 * @param {boolean}  p_override If set to true, p_fn will execute
                 *                   in the scope of p_obj
                 *
                 * @static
                 */
                onAvailable: function(p_id, p_fn, p_obj, p_override) {
                    onAvailStack.push( { id:         p_id,
                                         fn:         p_fn,
                                         obj:        p_obj,
                                         override:   p_override,
                                         checkReady: false    } );
                    retryCount = this.POLL_RETRYS;
                    this.startInterval();
                },

                /**
                 * Executes the supplied callback when the DOM is first usable.
                 *
                 * @method onDOMReady
                 *
                 * @param {function} p_fn what to execute when the element is found.
                 * @param {object}   p_obj an optional object to be passed back as
                 *                   a parameter to p_fn.
                 * @param {boolean}  p_scope If set to true, p_fn will execute
                 *                   in the scope of p_obj, if set to an object it
                 *                   will execute in the scope of that object
                 *
                 * @static
                 */
                onDOMReady: function(p_fn, p_obj, p_override) {
                    this.DOMReadyEvent.subscribe(p_fn, p_obj, p_override);
                },

                /**
                 * Works the same way as onAvailable, but additionally checks the
                 * state of sibling elements to determine if the content of the
                 * available element is safe to modify.
                 *
                 * @method onContentReady
                 *
                 * @param {string}   p_id the id of the element to look for.
                 * @param {function} p_fn what to execute when the element is ready.
                 * @param {object}   p_obj an optional object to be passed back as
                 *                   a parameter to p_fn.
                 * @param {boolean}  p_override If set to true, p_fn will execute
                 *                   in the scope of p_obj
                 *
                 * @static
                 */
                onContentReady: function(p_id, p_fn, p_obj, p_override) {
                    onAvailStack.push( { id:         p_id,
                                         fn:         p_fn,
                                         obj:        p_obj,
                                         override:   p_override,
                                         checkReady: true      } );

                    retryCount = this.POLL_RETRYS;
                    this.startInterval();
                },

                /**
                 * Appends an event handler
                 *
                 * @method addListener
                 *
                 * @param {Object}   el        The html element to assign the
                 *                             event to
                 * @param {String}   sType     The type of event to append
                 * @param {Function} fn        The method the event invokes
                 * @param {Object}   obj    An arbitrary object that will be
                 *                             passed as a parameter to the handler
                 * @param {boolean}  override  If true, the obj passed in becomes
                 *                             the execution scope of the listener
                 * @return {boolean} True if the action was successful or defered,
                 *                        false if one or more of the elements
                 *                        could not have the listener attached,
                 *                        or if the operation throws an exception.
                 * @static
                 */
                addListener: function(el, sType, fn, obj, override) {

                    if (!fn || !fn.call) {
                        // this.logger.debug("Error, function is not valid " + fn);
                        return false;
                    }

                    // The el argument can be an array of elements or element ids.
                    if ( this._isValidCollection(el)) {
                        var ok = true;
                        for (var i=0,len=el.length; i<len; ++i) {
                            ok = this.on(el[i],
                                           sType,
                                           fn,
                                           obj,
                                           override) && ok;
                        }
                        return ok;

                    } else if (typeof el == "string") {
                        var oEl = this.getEl(el);
                        // If the el argument is a string, we assume it is
                        // actually the id of the element.  If the page is loaded
                        // we convert el to the actual element, otherwise we
                        // defer attaching the event until onload event fires

                        // check to see if we need to delay hooking up the event
                        // until after the page loads.
                        if (oEl) {
                            el = oEl;
                        } else {
                            // defer adding the event until the element is available
                            this.onAvailable(el, function() {
                               YAHOO.util.Event.on(el, sType, fn, obj, override);
                            });

                            return true;
                        }
                    }

                    // Element should be an html element or an array if we get
                    // here.
                    if (!el) {
                        // this.logger.debug("unable to attach event " + sType);
                        return false;
                    }

                    // we need to make sure we fire registered unload events
                    // prior to automatically unhooking them.  So we hang on to
                    // these instead of attaching them to the window and fire the
                    // handles explicitly during our one unload event.
                    if ("unload" == sType && obj !== this) {
                        unloadListeners[unloadListeners.length] =
                                [el, sType, fn, obj, override];
                        return true;
                    }

                    // this.logger.debug("Adding handler: " + el + ", " + sType);

                    // if the user chooses to override the scope, we use the custom
                    // object passed in, otherwise the executing scope will be the
                    // HTML element that the event is registered on
                    var scope = el;
                    if (override) {
                        if (override === true) {
                            scope = obj;
                        } else {
                            scope = override;
                        }
                    }

                    // wrap the function so we can return the obj object when
                    // the event fires;
                    var wrappedFn = function(e) {
                            return fn.call(scope, YAHOO.util.Event.getEvent(e),
                                    obj);
                        };

                    var li = [el, sType, fn, wrappedFn, scope];
                    var index = listeners.length;
                    // cache the listener so we can try to automatically unload
                    listeners[index] = li;

                    if (this.useLegacyEvent(el, sType)) {
                        var legacyIndex = this.getLegacyIndex(el, sType);

                        // Add a new dom0 wrapper if one is not detected for this
                        // element
                        if ( legacyIndex == -1 ||
                                    el != legacyEvents[legacyIndex][0] ) {

                            legacyIndex = legacyEvents.length;
                            legacyMap[el.id + sType] = legacyIndex;

                            // cache the signature for the DOM0 event, and
                            // include the existing handler for the event, if any
                            legacyEvents[legacyIndex] =
                                [el, sType, el["on" + sType]];
                            legacyHandlers[legacyIndex] = [];

                            el["on" + sType] =
                                function(e) {
                                    YAHOO.util.Event.fireLegacyEvent(
                                        YAHOO.util.Event.getEvent(e), legacyIndex);
                                };
                        }

                        // add a reference to the wrapped listener to our custom
                        // stack of events
                        //legacyHandlers[legacyIndex].push(index);
                        legacyHandlers[legacyIndex].push(li);

                    } else {
                        try {
                            this._simpleAdd(el, sType, wrappedFn, false);
                        } catch(ex) {
                            // handle an error trying to attach an event.  If it fails
                            // we need to clean up the cache
                            this.lastError = ex;
                            this.removeListener(el, sType, fn);
                            return false;
                        }
                    }

                    return true;

                },

                /**
                 * When using legacy events, the handler is routed to this object
                 * so we can fire our custom listener stack.
                 * @method fireLegacyEvent
                 * @static
                 * @private
                 */
                fireLegacyEvent: function(e, legacyIndex) {
                    // this.logger.debug("fireLegacyEvent " + legacyIndex);
                    var ok=true,le,lh,li,scope,ret;

                    lh = legacyHandlers[legacyIndex];
                    for (var i=0,len=lh.length; i<len; ++i) {
                        li = lh[i];
                        if ( li && li[this.WFN] ) {
                            scope = li[this.ADJ_SCOPE];
                            ret = li[this.WFN].call(scope, e);
                            ok = (ok && ret);
                        }
                    }

                    // Fire the original handler if we replaced one.  We fire this
                    // after the other events to keep stopPropagation/preventDefault
                    // that happened in the DOM0 handler from touching our DOM2
                    // substitute
                    le = legacyEvents[legacyIndex];
                    if (le && le[2]) {
                        le[2](e);
                    }

                    return ok;
                },

                /**
                 * Returns the legacy event index that matches the supplied
                 * signature
                 * @method getLegacyIndex
                 * @static
                 * @private
                 */
                getLegacyIndex: function(el, sType) {
                    var key = this.generateId(el) + sType;
                    if (typeof legacyMap[key] == "undefined") {
                        return -1;
                    } else {
                        return legacyMap[key];
                    }
                },

                /**
                 * Logic that determines when we should automatically use legacy
                 * events instead of DOM2 events.  Currently this is limited to old
                 * Safari browsers with a broken preventDefault
                 * @method useLegacyEvent
                 * @static
                 * @private
                 */
                useLegacyEvent: function(el, sType) {
                    if (this.webkit && ("click"==sType || "dblclick"==sType)) {
                        var v = parseInt(this.webkit, 10);
                        if (!isNaN(v) && v<418) {
                            return true;
                        }
                    }
                    return false;
                },

                /**
                 * Removes an event handler
                 *
                 * @method removeListener
                 *
                 * @param {Object} el the html element or the id of the element to
                 * assign the event to.
                 * @param {String} sType the type of event to remove.
                 * @param {Function} fn the method the event invokes.  If fn is
                 * undefined, then all event handlers for the type of event are
                 * removed.
                 * @return {boolean} true if the unbind was successful, false
                 * otherwise.
                 * @static
                 */
                removeListener: function(el, sType, fn) {
                    var i, len;

                    // The el argument can be a string
                    if (typeof el == "string") {
                        el = this.getEl(el);
                    // The el argument can be an array of elements or element ids.
                    } else if ( this._isValidCollection(el)) {
                        var ok = true;
                        for (i=0,len=el.length; i<len; ++i) {
                            ok = ( this.removeListener(el[i], sType, fn) && ok );
                        }
                        return ok;
                    }

                    if (!fn || !fn.call) {
                        // this.logger.debug("Error, function is not valid " + fn);
                        //return false;
                        return this.purgeElement(el, false, sType);
                    }

                    if ("unload" == sType) {

                        for (i=0, len=unloadListeners.length; i<len; i++) {
                            var li = unloadListeners[i];
                            if (li &&
                                li[0] == el &&
                                li[1] == sType &&
                                li[2] == fn) {
                                    unloadListeners.splice(i, 1);
                                    return true;
                            }
                        }

                        return false;
                    }

                    var cacheItem = null;

                    // The index is a hidden parameter; needed to remove it from
                    // the method signature because it was tempting users to
                    // try and take advantage of it, which is not possible.
                    var index = arguments[3];

                    if ("undefined" == typeof index) {
                        index = this._getCacheIndex(el, sType, fn);
                    }

                    if (index >= 0) {
                        cacheItem = listeners[index];
                    }

                    if (!el || !cacheItem) {
                        // this.logger.debug("cached listener not found");
                        return false;
                    }

                    // this.logger.debug("Removing handler: " + el + ", " + sType);

                    if (this.useLegacyEvent(el, sType)) {
                        var legacyIndex = this.getLegacyIndex(el, sType);
                        var llist = legacyHandlers[legacyIndex];
                        if (llist) {
                            for (i=0, len=llist.length; i<len; ++i) {
                                li = llist[i];
                                if (li &&
                                    li[this.EL] == el &&
                                    li[this.TYPE] == sType &&
                                    li[this.FN] == fn) {
                                        llist.splice(i, 1);
                                        break;
                                }
                            }
                        }

                    } else {
                        try {
                            this._simpleRemove(el, sType, cacheItem[this.WFN], false);
                        } catch(ex) {
                            this.lastError = ex;
                            return false;
                        }
                    }

                    // removed the wrapped handler
                    delete listeners[index][this.WFN];
                    delete listeners[index][this.FN];
                    listeners.splice(index, 1);

                    return true;

                },

                /**
                 * Returns the event's target element
                 * @method getTarget
                 * @param {Event} ev the event
                 * @param {boolean} resolveTextNode when set to true the target's
                 *                  parent will be returned if the target is a
                 *                  text node.  @deprecated, the text node is
                 *                  now resolved automatically
                 * @return {HTMLElement} the event's target
                 * @static
                 */
                getTarget: function(ev, resolveTextNode) {
                    var t = ev.target || ev.srcElement;
                    return this.resolveTextNode(t);
                },

                /**
                 * In some cases, some browsers will return a text node inside
                 * the actual element that was targeted.  This normalizes the
                 * return value for getTarget and getRelatedTarget.
                 * @method resolveTextNode
                 * @param {HTMLElement} node node to resolve
                 * @return {HTMLElement} the normized node
                 * @static
                 */
                resolveTextNode: function(node) {
                    // if (node && node.nodeName &&
                            // "#TEXT" == node.nodeName.toUpperCase()) {
                    if (node && 3 == node.nodeType) {
                        return node.parentNode;
                    } else {
                        return node;
                    }
                },

                /**
                 * Returns the event's pageX
                 * @method getPageX
                 * @param {Event} ev the event
                 * @return {int} the event's pageX
                 * @static
                 */
                getPageX: function(ev) {
                    var x = ev.pageX;
                    if (!x && 0 !== x) {
                        x = ev.clientX || 0;

                        if ( this.isIE ) {
                            x += this._getScrollLeft();
                        }
                    }

                    return x;
                },

                /**
                 * Returns the event's pageY
                 * @method getPageY
                 * @param {Event} ev the event
                 * @return {int} the event's pageY
                 * @static
                 */
                getPageY: function(ev) {
                    var y = ev.pageY;
                    if (!y && 0 !== y) {
                        y = ev.clientY || 0;

                        if ( this.isIE ) {
                            y += this._getScrollTop();
                        }
                    }

                    return y;
                },

                /**
                 * Returns the pageX and pageY properties as an indexed array.
                 * @method getXY
                 * @param {Event} ev the event
                 * @return {[x, y]} the pageX and pageY properties of the event
                 * @static
                 */
                getXY: function(ev) {
                    return [this.getPageX(ev), this.getPageY(ev)];
                },

                /**
                 * Returns the event's related target
                 * @method getRelatedTarget
                 * @param {Event} ev the event
                 * @return {HTMLElement} the event's relatedTarget
                 * @static
                 */
                getRelatedTarget: function(ev) {
                    var t = ev.relatedTarget;
                    if (!t) {
                        if (ev.type == "mouseout") {
                            t = ev.toElement;
                        } else if (ev.type == "mouseover") {
                            t = ev.fromElement;
                        }
                    }

                    return this.resolveTextNode(t);
                },

                /**
                 * Returns the time of the event.  If the time is not included, the
                 * event is modified using the current time.
                 * @method getTime
                 * @param {Event} ev the event
                 * @return {Date} the time of the event
                 * @static
                 */
                getTime: function(ev) {
                    if (!ev.time) {
                        var t = new Date().getTime();
                        try {
                            ev.time = t;
                        } catch(ex) {
                            this.lastError = ex;
                            return t;
                        }
                    }

                    return ev.time;
                },

                /**
                 * Convenience method for stopPropagation + preventDefault
                 * @method stopEvent
                 * @param {Event} ev the event
                 * @static
                 */
                stopEvent: function(ev) {
                    this.stopPropagation(ev);
                    this.preventDefault(ev);
                },

                /**
                 * Stops event propagation
                 * @method stopPropagation
                 * @param {Event} ev the event
                 * @static
                 */
                stopPropagation: function(ev) {
                    if (ev.stopPropagation) {
                        ev.stopPropagation();
                    } else {
                        ev.cancelBubble = true;
                    }
                },

                /**
                 * Prevents the default behavior of the event
                 * @method preventDefault
                 * @param {Event} ev the event
                 * @static
                 */
                preventDefault: function(ev) {
                    if (ev.preventDefault) {
                        ev.preventDefault();
                    } else {
                        ev.returnValue = false;
                    }
                },

                /**
                 * Finds the event in the window object, the caller's arguments, or
                 * in the arguments of another method in the callstack.  This is
                 * executed automatically for events registered through the event
                 * manager, so the implementer should not normally need to execute
                 * this function at all.
                 * @method getEvent
                 * @param {Event} e the event parameter from the handler
                 * @return {Event} the event
                 * @static
                 */
                getEvent: function(e) {
                    var ev = e || window.event;

                    if (!ev) {
                        var c = this.getEvent.caller;
                        while (c) {
                            ev = c.arguments[0];
                            if (ev && Event == ev.constructor) {
                                break;
                            }
                            c = c.caller;
                        }
                    }

                    return ev;
                },

                /**
                 * Returns the charcode for an event
                 * @method getCharCode
                 * @param {Event} ev the event
                 * @return {int} the event's charCode
                 * @static
                 */
                getCharCode: function(ev) {
                    return ev.charCode || ev.keyCode || 0;
                },

                /**
                 * Locating the saved event handler data by function ref
                 *
                 * @method _getCacheIndex
                 * @static
                 * @private
                 */
                _getCacheIndex: function(el, sType, fn) {
                    for (var i=0,len=listeners.length; i<len; ++i) {
                        var li = listeners[i];
                        if ( li                 &&
                             li[this.FN] == fn  &&
                             li[this.EL] == el  &&
                             li[this.TYPE] == sType ) {
                            return i;
                        }
                    }

                    return -1;
                },

                /**
                 * Generates an unique ID for the element if it does not already
                 * have one.
                 * @method generateId
                 * @param el the element to create the id for
                 * @return {string} the resulting id of the element
                 * @static
                 */
                generateId: function(el) {
                    var id = el.id;

                    if (!id) {
                        id = "yuievtautoid-" + counter;
                        ++counter;
                        el.id = id;
                    }

                    return id;
                },

                /**
                 * We want to be able to use getElementsByTagName as a collection
                 * to attach a group of events to.  Unfortunately, different
                 * browsers return different types of collections.  This function
                 * tests to determine if the object is array-like.  It will also
                 * fail if the object is an array, but is empty.
                 * @method _isValidCollection
                 * @param o the object to test
                 * @return {boolean} true if the object is array-like and populated
                 * @static
                 * @private
                 */
                _isValidCollection: function(o) {
                    return ( o                    && // o is something
                             o.length             && // o is indexed
                             typeof o != "string" && // o is not a string
                             !o.tagName           && // o is not an HTML element
                             !o.alert             && // o is not a window
                             typeof o[0] != "undefined" );

                },

                /**
                 * @private
                 * @property elCache
                 * DOM element cache
                 * @static
                 * @deprecated Elements are not cached any longer
                 */
                elCache: {},

                /**
                 * We cache elements bound by id because when the unload event
                 * fires, we can no longer use document.getElementById
                 * @method getEl
                 * @static
                 * @private
                 * @deprecated Elements are not cached any longer
                 */
                getEl: function(id) {
                    return document.getElementById(id);
                },

                /**
                 * Clears the element cache
                 * @deprecated Elements are not cached any longer
                 * @method clearCache
                 * @static
                 * @private
                 */
                clearCache: function() { },

                /**
                 * Custom event the fires when the dom is initially usable
                 * @event DOMReadyEvent
                 */
                DOMReadyEvent: new YAHOO.util.CustomEvent("DOMReady", this),

                /**
                 * hook up any deferred listeners
                 * @method _load
                 * @static
                 * @private
                 */
                _load: function(e) {
                    loadComplete = true;
                    var EU = YAHOO.util.Event;

                    // just in case DOMReady did not go off for some reason
                    EU._ready();

                    // Remove the listener to assist with the IE memory issue, but not
                    // for other browsers because FF 1.0x does not like it.
                    if (this.isIE) {
                        EU._simpleRemove(window, "load", EU._load);
                    }
                },

                /**
                 * Fires the DOMReady event listeners the first time the document is
                 * usable.
                 * @method _ready
                 * @static
                 * @private
                 */
                _ready: function(e) {
                    if (!DOMReady) {
                        DOMReady=true;
                        var EU = YAHOO.util.Event;

                        // Fire the content ready custom event
                        EU.DOMReadyEvent.fire();

                        // Remove the DOMContentLoaded (FF/Opera)
                        EU._simpleRemove(document, "DOMContentLoaded", EU._ready);
                    }
                },

                /**
                 * Polling function that runs before the onload event fires,
                 * attempting to attach to DOM Nodes as soon as they are
                 * available
                 * @method _tryPreloadAttach
                 * @static
                 * @private
                 */
                _tryPreloadAttach: function() {

                    if (this.locked) {
                        return false;
                    }

                    if (this.isIE && !DOMReady) {
                        return false;
                    }

                    this.locked = true;

                    // this.logger.debug("tryPreloadAttach");

                    // keep trying until after the page is loaded.  We need to
                    // check the page load state prior to trying to bind the
                    // elements so that we can be certain all elements have been
                    // tested appropriately
                    var tryAgain = !loadComplete;
                    if (!tryAgain) {
                        tryAgain = (retryCount > 0);
                    }

                    // onAvailable
                    var notAvail = [];

                    var executeItem = function (el, item) {
                        var scope = el;
                        if (item.override) {
                            if (item.override === true) {
                                scope = item.obj;
                            } else {
                                scope = item.override;
                            }
                        }
                        item.fn.call(scope, item.obj);
                    };

                    var i,len,item,el;

                    // onAvailable
                    for (i=0,len=onAvailStack.length; i<len; ++i) {
                        item = onAvailStack[i];
                        if (item && !item.checkReady) {
                            el = this.getEl(item.id);
                            if (el) {
                                executeItem(el, item);
                                onAvailStack[i] = null;
                            } else {
                                notAvail.push(item);
                            }
                        }
                    }

                    // onContentReady
                    for (i=0,len=onAvailStack.length; i<len; ++i) {
                        item = onAvailStack[i];
                        if (item && item.checkReady) {
                            el = this.getEl(item.id);

                            if (el) {
                                // The element is available, but not necessarily ready
                                // @todo should we test parentNode.nextSibling?
                                if (loadComplete || el.nextSibling) {
                                    executeItem(el, item);
                                    onAvailStack[i] = null;
                                }
                            } else {
                                notAvail.push(item);
                            }
                        }
                    }

                    retryCount = (notAvail.length === 0) ? 0 : retryCount - 1;

                    if (tryAgain) {
                        // we may need to strip the nulled out items here
                        this.startInterval();
                    } else {
                        clearInterval(this._interval);
                        this._interval = null;
                    }

                    this.locked = false;

                    return true;

                },

                /**
                 * Removes all listeners attached to the given element via addListener.
                 * Optionally, the node's children can also be purged.
                 * Optionally, you can specify a specific type of event to remove.
                 * @method purgeElement
                 * @param {HTMLElement} el the element to purge
                 * @param {boolean} recurse recursively purge this element's children
                 * as well.  Use with caution.
                 * @param {string} sType optional type of listener to purge. If
                 * left out, all listeners will be removed
                 * @static
                 */
                purgeElement: function(el, recurse, sType) {
                    var elListeners = this.getListeners(el, sType);
                    if (elListeners) {
                        for (var i=0,len=elListeners.length; i<len ; ++i) {
                            var l = elListeners[i];
                            // can't use the index on the changing collection
                            //this.removeListener(el, l.type, l.fn, l.index);
                            this.removeListener(el, l.type, l.fn);
                        }
                    }

                    if (recurse && el && el.childNodes) {
                        for (i=0,len=el.childNodes.length; i<len ; ++i) {
                            this.purgeElement(el.childNodes[i], recurse, sType);
                        }
                    }
                },

                /**
                 * Returns all listeners attached to the given element via addListener.
                 * Optionally, you can specify a specific type of event to return.
                 * @method getListeners
                 * @param el {HTMLElement} the element to inspect
                 * @param sType {string} optional type of listener to return. If
                 * left out, all listeners will be returned
                 * @return {Object} the listener. Contains the following fields:
                 * &nbsp;&nbsp;type:   (string)   the type of event
                 * &nbsp;&nbsp;fn:     (function) the callback supplied to addListener
                 * &nbsp;&nbsp;obj:    (object)   the custom object supplied to addListener
                 * &nbsp;&nbsp;adjust: (boolean)  whether or not to adjust the default scope
                 * &nbsp;&nbsp;index:  (int)      its position in the Event util listener cache
                 * @static
                 */
                getListeners: function(el, sType) {
                    var results=[], searchLists;
                    if (!sType) {
                        searchLists = [listeners, unloadListeners];
                    } else if (sType == "unload") {
                        searchLists = [unloadListeners];
                    } else {
                        searchLists = [listeners];
                    }

                    for (var j=0;j<searchLists.length; ++j) {
                        var searchList = searchLists[j];
                        if (searchList && searchList.length > 0) {
                            for (var i=0,len=searchList.length; i<len ; ++i) {
                                var l = searchList[i];
                                if ( l  && l[this.EL] === el &&
                                        (!sType || sType === l[this.TYPE]) ) {
                                    results.push({
                                        type:   l[this.TYPE],
                                        fn:     l[this.FN],
                                        obj:    l[this.OBJ],
                                        adjust: l[this.ADJ_SCOPE],
                                        index:  i
                                    });
                                }
                            }
                        }
                    }

                    return (results.length) ? results : null;
                },

                /**
                 * Removes all listeners registered by pe.event.  Called
                 * automatically during the unload event.
                 * @method _unload
                 * @static
                 * @private
                 */
                _unload: function(e) {

                    var EU = YAHOO.util.Event, i, j, l, len, index;

                    for (i=0,len=unloadListeners.length; i<len; ++i) {
                        l = unloadListeners[i];
                        if (l) {
                            var scope = window;
                            if (l[EU.ADJ_SCOPE]) {
                                if (l[EU.ADJ_SCOPE] === true) {
                                    scope = l[EU.OBJ];
                                } else {
                                    scope = l[EU.ADJ_SCOPE];
                                }
                            }
                            l[EU.FN].call(scope, EU.getEvent(e), l[EU.OBJ] );
                            unloadListeners[i] = null;
                            l=null;
                            scope=null;
                        }
                    }

                    unloadListeners = null;

                    if (listeners && listeners.length > 0) {
                        j = listeners.length;
                        while (j) {
                            index = j-1;
                            l = listeners[index];
                            if (l) {
                                EU.removeListener(l[EU.EL], l[EU.TYPE],
                                        l[EU.FN], index);
                            }
                            j = j - 1;
                        }
                        l=null;

                        EU.clearCache();
                    }

                    for (i=0,len=legacyEvents.length; i<len; ++i) {
                        // dereference the element
                        //delete legacyEvents[i][0];
                        legacyEvents[i][0] = null;

                        // delete the array item
                        //delete legacyEvents[i];
                        legacyEvents[i] = null;
                    }

                    legacyEvents = null;

                    EU._simpleRemove(window, "unload", EU._unload);

                },

                /**
                 * Returns scrollLeft
                 * @method _getScrollLeft
                 * @static
                 * @private
                 */
                _getScrollLeft: function() {
                    return this._getScroll()[1];
                },

                /**
                 * Returns scrollTop
                 * @method _getScrollTop
                 * @static
                 * @private
                 */
                _getScrollTop: function() {
                    return this._getScroll()[0];
                },

                /**
                 * Returns the scrollTop and scrollLeft.  Used to calculate the
                 * pageX and pageY in Internet Explorer
                 * @method _getScroll
                 * @static
                 * @private
                 */
                _getScroll: function() {
                    var dd = document.documentElement, db = document.body;
                    if (dd && (dd.scrollTop || dd.scrollLeft)) {
                        return [dd.scrollTop, dd.scrollLeft];
                    } else if (db) {
                        return [db.scrollTop, db.scrollLeft];
                    } else {
                        return [0, 0];
                    }
                },

                /**
                 * Used by old versions of CustomEvent, restored for backwards
                 * compatibility
                 * @method regCE
                 * @private
                 */
                regCE: function() {
                    // does nothing
                },

                /**
                 * Adds a DOM event directly without the caching, cleanup, scope adj, etc
                 *
                 * @method _simpleAdd
                 * @param {HTMLElement} el      the element to bind the handler to
                 * @param {string}      sType   the type of event handler
                 * @param {function}    fn      the callback to invoke
                 * @param {boolen}      capture capture or bubble phase
                 * @static
                 * @private
                 */
                _simpleAdd: function () {
                    if (window.addEventListener) {
                        return function(el, sType, fn, capture) {
                            el.addEventListener(sType, fn, (capture));
                        };
                    } else if (window.attachEvent) {
                        return function(el, sType, fn, capture) {
                            el.attachEvent("on" + sType, fn);
                        };
                    } else {
                        return function(){};
                    }
                }(),

                /**
                 * Basic remove listener
                 *
                 * @method _simpleRemove
                 * @param {HTMLElement} el      the element to bind the handler to
                 * @param {string}      sType   the type of event handler
                 * @param {function}    fn      the callback to invoke
                 * @param {boolen}      capture capture or bubble phase
                 * @static
                 * @private
                 */
                _simpleRemove: function() {
                    if (window.removeEventListener) {
                        return function (el, sType, fn, capture) {
                            el.removeEventListener(sType, fn, (capture));
                        };
                    } else if (window.detachEvent) {
                        return function (el, sType, fn) {
                            el.detachEvent("on" + sType, fn);
                        };
                    } else {
                        return function(){};
                    }
                }()
            };

        }();

        (function() {
            var EU = YAHOO.util.Event;

            /**
             * YAHOO.util.Event.on is an alias for addListener
             * @method on
             * @see addListener
             * @static
             */
            EU.on = EU.addListener;

            /////////////////////////////////////////////////////////////
            // DOMReady
            // based on work by: Dean Edwards/John Resig/Matthias Miller

            // Internet Explorer: use the readyState of a defered script.
            // This isolates what appears to be a safe moment to manipulate
            // the DOM prior to when the document's readyState suggests
            // it is safe to do so.
            if (EU.isIE) {

                document.write(
    '<scr' + 'ipt id="_yui_eu_dr" defer="true" src="//:"></script>');

                var el = document.getElementById("_yui_eu_dr");
                el.onreadystatechange = function() {
                    if ("complete" == this.readyState) {
                        this.parentNode.removeChild(this);
                        YAHOO.util.Event._ready();
                    }
                };

                el=null;

                // Process onAvailable/onContentReady items when when the
                // DOM is ready.
                YAHOO.util.Event.onDOMReady(
                        YAHOO.util.Event._tryPreloadAttach,
                        YAHOO.util.Event, true);

            // Safari: The document's readyState in Safari currently will
            // change to loaded/complete before images are loaded.
            } else if (EU.webkit) {

                EU._drwatch = setInterval(function(){
                    var rs=document.readyState;
                    if ("loaded" == rs || "complete" == rs) {
                        clearInterval(EU._drwatch);
                        EU._drwatch = null;
                        EU._ready();
                    }
                }, EU.POLL_INTERVAL);

            // FireFox and Opera: These browsers provide a event for this
            // moment.
            } else {

                EU._simpleAdd(document, "DOMContentLoaded", EU._ready);

            }
            /////////////////////////////////////////////////////////////

            if (document && document.body) {
                EU._load();
            } else {
                EU._simpleAdd(window, "load", EU._load);
            }
            EU._simpleAdd(window, "unload", EU._unload);
            EU._tryPreloadAttach();
        })();
    }

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