Geo-Tag中的jQuery错误：a.getAttribute不是函数

Question

function setMarkers（map，beaches，titles，storeinfo）{

            for (var i = 0; i < beaches.length; i++) {

                ad = titles[i].toString();
                var  beache =  beaches[i].toString().split(',');
                lt = beache[0];
                lg = beache[1];
                var myLatLng = new google.maps.LatLng(lt,lg);
                j=i+1;
                var marker = new google.maps.Marker({ position: myLatLng,   map: map,  title:ad,  zIndex:j, icon: 'http://chart.googleapis.com/chart?chst=d_map_pin_letter&chld='+j+'|FC6355|000000&.png%3f'});

                google.maps.event.addDomListener(marker, 'mouseover', function (event) {

               var m =$(this).attr("zIndex"); //In this point,I am getting a error :"a.getAttribute is not a function"
                var html = "<p>My Store</p>" ; 
                html += "<p><i>"+storeinfo[m]+"</i></p>";
                html += "<p style='font-size:10px'>"+titles+"</p>";
                pixelCoordsCenter = map.getProjection().fromLatLngToPoint(event.latLng);
                showInfowWindow(html,pixelCoordsCenter,event);
                highlightedMarker = 1;
            });

             google.maps.event.addDomListener(marker, 'mouseout', function (event) {
                $("#mapPopup").hide();
            });
            }
        }  

您好， 这里有问题： $（本）.attr（ “zIndex的”）; 错误：a.getAttribute不是函数 请帮帮我......