js得到 event对象 （IE,FF）

js得到 event对象
function getEvent() {
if (document.all) {
return window.event;//如果是ie
}
func = getEvent.caller;//如果是ff
while (func != null) {
var arg0 = func.arguments[0];
if (arg0) {
if ((arg0.constructor == Event || arg0.constructor == MouseEvent) || (typeof (arg0) == "object" && arg0.preventDefault && arg0.stopPropagation)) {
return arg0;
}
}
func = func.caller;
}
return null;
}