javascript兼容FF的onmouseenter和onmouseleave的代码_javascript技巧

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IE下有 onmouseenter和onmouseleave来解决。
可惜ff就没有。 我再想 ， 为什么这么好的功能，为什么ff不引用呢？
还有ie中的onpropertychange ，哎，ff中都没有。。。

对比例子中引入了一段js ，来兼容FF的onmouseenter和onmouseleave. ：

代码如下:

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;
}
};
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