javascript 兼容FF的onmouseenter和onmouseleave

<script>
var xb = {
	evtHash: [],
	ieGetUniqueID: function(_elem) {
		if (_elem === window) {
			return 'theWindow';
		} else if (_elem === document) {
			return 'theDocument';
		} else {
			return _elem.uniqueID;
		}
	},
	addEvent: function(_elem, _evtName, _fn, _useCapture) {
		if (typeof _elem.addEventListener != 'undefined') {
			if (_evtName == 'mouseenter') {
				_elem.addEventListener('mouseover', xb.mouseEnter(_fn), _useCapture);
			} else if (_evtName == 'mouseleave') {
				_elem.addEventListener('mouseout', xb.mouseEnter(_fn), _useCapture);
			} else {
				_elem.addEventListener(_evtName, _fn, _useCapture);
			}
		} else if (typeof _elem.attachEvent != 'undefined') {
			var key = '{FNKEY::obj_' + xb.ieGetUniqueID(_elem) + '::evt_' + _evtName + '::fn_' + _fn + '}';
			var f = xb.evtHash[key];
			if (typeof f != 'undefined') {
				return;
			}
			f = function() {
				_fn.call(_elem);
			};
			xb.evtHash[key] = f;
			_elem.attachEvent('on' + _evtName, f); // attach unload event to the window to clean up possibly IE memory leaks 
			window.attachEvent('onunload',
			function() {
				_elem.detachEvent('on' + _evtName, f);
			});
			key = null; //f = null; /* DON'T null this out, or we won't be able to detach it */ 
		} else {
			_elem['on' + _evtName] = _fn;
		}
	},
	removeEvent: function(_elem, _evtName, _fn, _useCapture) {
		if (typeof _elem.removeEventListener != 'undefined') {
			_elem.removeEventListener(_evtName, _fn, _useCapture);
		} else if (typeof _elem.detachEvent != 'undefined') {
			var key = '{FNKEY::obj_' + xb.ieGetUniqueID(_elem) + '::evt' + _evtName + '::fn_' + _fn + '}';
			var f = xb.evtHash[key];
			if (typeof f != 'undefined') {
				_elem.detachEvent('on' + _evtName, f);
				delete xb.evtHash[key];
			}
			key = null; //f = null; /* DON'T null this out, or we won't be able to detach it */ 
		}
	},
	mouseEnter: function(_pFn) {
		return function(_evt) {
			var relTarget = _evt.relatedTarget;
			if (this == relTarget || xb.isAChildOf(this, relTarget)) {
				return;
			}
			_pFn.call(this, _evt);
		}
	},
	isAChildOf: function(_parent, _child) {
		if (_parent == _child) {
			return false
		};
		while (_child && _child != _parent) {
			_child = _child.parentNode;
		}
		return _child == _parent;
	}
};

  </script>