获得Event对象

function getEvent(){     //同时兼容ie和ff的写法
         if(document.all)    return window.event;        
         func=getEvent.caller;            
        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;
 }