# Yahoo! UI Library

### event 3.0.0

Yahoo! UI Library > event > mouseentermouseleave.js (source view)
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    /**
     * Adds support for mouseenter/mouseleave events
     * @module event
     * @submodule event-mouseenter
     */
    var Event = Y.Event,
    	Lang = Y.Lang,

    	plugins = Y.Env.evt.plugins,

    	listeners = {},

    	eventConfig = {

        	on: function(type, fn, el) {

    		    var args = Y.Array(arguments, 0, true),
    				element = el,
    				availHandle;

    			if (Lang.isString(el)) {

    				//	Need to use Y.all because if el is a string it could be a
    				//	selector that returns a NodeList

    				element = Y.all(el);

    				if (element.size() === 0) { // Not found, check using onAvailable

    		            availHandle = Event.onAvailable(el, function() {

    		                availHandle.handle = Y.on.apply(Y, args);

    		            }, Event, true, false);

    					return availHandle;

    				}

    			}

    	        var sDOMEvent = (type === "mouseenter") ? "mouseover" : "mouseout",

    				//	The name of the custom event
    				sEventName = type + ":" + Y.stamp(element) + sDOMEvent,

    				listener = listeners[sEventName],

    				domEventHandle,

    				ceHandle,

    				nListeners;

    			//	Bind an actual DOM event listener that will call the
    			//	the custom event
    			if (!listener) {

    				domEventHandle = Y.on(sDOMEvent, Y.rbind(Event._fireMouseEnter, Y, sEventName), element);

    				//	Hook into the _delete method for the Custom Event wrapper of this
    				//	DOM Event in order to clean up the 'listeners' map and unsubscribe
    				//	the associated Custom Event listeners fired by this DOM event
    				//	listener if/when the user calls "purgeElement" OR removes all
    				//	listeners of the Custom Event.

    				Y.after(function (sub) {

    					if (domEventHandle.sub == sub) {

    						//	Delete this event from the map of known mouseenter
    						//	and mouseleave listeners
    						delete listeners[sEventName];

    						Y.log("DOM event listener associated with the " + sEventName + " Custom Event removed.  Removing all " + sEventName + " listeners.", "info", "Event");

    						//	Unsubscribe all listeners of the Custom Event fired
    						//	by this DOM event.
    						Y.detachAll(sEventName);

    					}

    				}, domEventHandle.evt, "_delete");

    				listener = {};
    				listener.handle = domEventHandle;

    				listeners[sEventName] = listener;

    			}

    			nListeners = listener.count;

    			listener.count = nListeners ? (nListeners + 1) : 1;

    	        args[0] = sEventName;

    	        // Remove the element from the args
    			args.splice(2, 1);

    	        // Subscribe to the custom event
    	        ceHandle = Y.on.apply(Y, args);

    			//	Hook into the detach method of the handle in order to clean up the
    			//	'listeners' map and remove the associated DOM event handler
    			//	responsible for firing this Custom Event if all listener for this
    			//	event have been removed.

    			Y.after(function () {

    				listener.count = (listener.count - 1);

    				if (listener.count === 0) {
    					Y.log("No more listeners for the " + sEventName + " Custom Event.  Removing its associated DOM event listener.", "info", "Event");
    					listener.handle.detach();
    				}

    			}, ceHandle, "detach");

    			return ceHandle;

    	    }

    	};

    Event._fireMouseEnter = function (e, eventName) {

    	var relatedTarget = e.relatedTarget,
    		currentTarget = e.currentTarget;

    	if (currentTarget !== relatedTarget &&
    		!currentTarget.contains(relatedTarget)) {

    		Y.publish(eventName, {
                   contextFn: function() {
                       return currentTarget;
                   }
               });

    		Y.fire(eventName, e);

    	}

    };

    /**
     * Sets up a "mouseenter" listener&#151;a listener that is called the first time
     * the user's mouse enters the specified element(s).
     *
     * @event mouseenter
     * @param type {string} "mouseenter"
     * @param fn {function} The method the event invokes.
     * @param el {string|node} The element(s) to assign the listener to.
     * @param spec {string} Optional.  String representing a selector that must
     * match the target of the event in order for the listener to be called.
     * @return {EventHandle} the detach handle
     * @for YUI
     */
    plugins.mouseenter = eventConfig;

    /**
    * Sets up a "mouseleave" listener&#151;a listener that is called the first time
    * the user's mouse leaves the specified element(s).
    *
    * @event mouseleave
    * @param type {string} "mouseleave"
    * @param fn {function} The method the event invokes.
    * @param el {string|node} The element(s) to assign the listener to.
    * @param spec {string} Optional.  String representing a selector that must
    * match the target of the event in order for the listener to be called.
    * @return {EventHandle} the detach handle
    * @for YUI
     */
    plugins.mouseleave = eventConfig;

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