event.js

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                if (!t) {
                    if (ev.type == "mouseout") {
                        t = ev.toElement;
                    } else if (ev.type == "mouseover") {
                        t = ev.fromElement;
                    }
                }

                return t;
            },

            /**
             * Returns the time of the event.  If the time is not included, the
             * event is modified using the current time.
             * @param {Event} ev the event
             * @return {Date} the time of the event
             */
            getTime: function(ev) {
                if (!ev.time) {
                    var t = new Date().getTime();
                    try {
                        ev.time = t;
                    } catch(e) { 
                        // can't set the time property  
                        return t;
                    }
                }

                return ev.time;
            },

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

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

            /**
             * Prevents the default behavior of the event
             * @param {Event} ev the event
             */
            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.
             * @param {Event} the event parameter from the handler
             * @return {Event} the event 
             */
            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
             * @param {Event} ev the event
             * @return {int} the event's charCode
             */
            getCharCode: function(ev) {
                return ev.charCode || ((ev.type == "keypress") ? ev.keyCode : 0);
            },

            /**
             * @private
             * Locating the saved event handler data by function ref
             */
            _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.
             * @param el the element
             * @return {string} the id of the element
             */
            generateId: function(el) {
                var id = el.id;

                if (!id) {
                    id = "yuievtautoid-" + (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.
             * @param o the object to test
             * @return {boolean} true if the object is array-like and populated
             * @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
             * DOM element cache
             */
            elCache: {},

            /**
             * We cache elements bound by id because when the unload event 
             * fires, we can no longer use document.getElementById
             * @private
             */
            getEl: function(id) {
                return document.getElementById(id);
            },

            /**
             * Clears the element cache
             * @deprecated
             * @private
             */
            clearCache: function() { },

            /**
             * Called by CustomEvent instances to provide a handle to the 
             * event * that can be removed later on.  Should be package 
             * protected.
             * @private
             */
            regCE: function(ce) {
                customEvents.push(ce);
            },

            /**
             * @private
             * hook up any deferred listeners
             */
            _load: function(e) {
                loadComplete = true;
            },

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

                if (this.locked) {
                    return false;
                }

                this.locked = true;


                // 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);
                }

                // Delayed listeners
                var stillDelayed = [];

                for (var i=0,len=delayedListeners.length; i<len; ++i) {
                    var d = delayedListeners[i];
                    // There may be a race condition here, so we need to 
                    // verify the array element is usable.
                    if (d) {

                        // el will be null if document.getElementById did not
                        // work
                        var el = this.getEl(d[this.EL]);

                        if (el) {
                            this.on(el, d[this.TYPE], d[this.FN], 
                                    d[this.SCOPE], d[this.ADJ_SCOPE]);
                            delete delayedListeners[i];
                        } else {
                            stillDelayed.push(d);
                        }
                    }
                }

                delayedListeners = stillDelayed;

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

                        if (el) {
                            var scope = (item.override) ? item.obj : el;
                            item.fn.call(scope, item.obj);
                            delete onAvailStack[i];
                        } else {
                            notAvail.push(item);
                        }
                    }
                }

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

                if (tryAgain) {
                    this.startTimeout();
                }

                this.locked = false;

            },

            /**
             * Removes all listeners registered by pe.event.  Called 
             * automatically during the unload event.
             * @private
             */
            _unload: function(e, me) {
                for (var i=0,len=unloadListeners.length; i<len; ++i) {
                    var l = unloadListeners[i];
                    if (l) {
                        var scope = (l[this.ADJ_SCOPE]) ? l[this.SCOPE]: window;
                        l[this.FN].call(scope, this.getEvent(e), l[this.SCOPE] );
                    }
                }

                if (listeners && listeners.length > 0) {
                    for (i=0,len=listeners.length; i<len ; ++i) {
                        l = listeners[i];
                        if (l) {
                            this.removeListener(l[this.EL], l[this.TYPE], 
                                    l[this.FN], i);
                        }
                    }

                    this.clearCache();
                }

                for (i=0,len=customEvents.length; i<len; ++i) {
                    customEvents[i].unsubscribeAll();
                    delete customEvents[i];
                }

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

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

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

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

    /**
     * @private
     */
    YAHOO.util.Event.on = YAHOO.util.Event.addListener;

    if (document && document.body) {
        YAHOO.util.Event._load();
    } else {
        YAHOO.util.Event.on(window, "load", YAHOO.util.Event._load, 
                YAHOO.util.Event, true);
    }

    YAHOO.util.Event.on(window, "unload", YAHOO.util.Event._unload, 
                YAHOO.util.Event, true);

    YAHOO.util.Event._tryPreloadAttach();

}