IE Firefox兼容Enter代替Tab的javaScript

document.onkeydown=function(evt)
              {
               var isie = (document.all) ? true : false;
               var key;
               var srcobj;
               if (isie)
                {
                  key = event.keyCode;
                  srcobj=event.srcElement;
                  }
               else
                {
                  key = evt.which;
                  srcobj=evt.target;
                  }              
                 if(key==13 && srcobj.type!='button' && srcobj.type!='submit' &&srcobj.type!='reset' && srcobj.type!='textarea' && srcobj.type!='')                
                  {
                   if(isie)
                    {
                     event.keyCode=9;
                    }
                   else
                    {                       
                     var el=getNextElement(evt.target);
                             if (el.type!='hidden')
                                 el.focus();
                             else
                                while (el.type=='hidden')
                                    el=getNextElement(el);
                                 el.focus();
                             return false;
                    }
                  }
               }               
                function getNextElement (field) {
                   var form = field.form;
                   for (var e = 0; e < form.elements.length; e++) {
                     if (field == form.elements[e])
                         break;
                    }
                   return form.elements[++e % form.elements.length];
                  }