jquery json loop through data - just cant figure this out

I have a button on a pge thats fetches json data from a php page,

the data seems to arrive ok but i have gone through hundreds of examples and i just cant seem to reference the returned data, here is my script:

EDITED SCRIPT from previous comments

 $('#geo_batch').click(function (){
            var ajax_load = "<label><img src='/images/icons/loadinfo.gif' alt='saving location...' /> Loading data...</label>";
            $("#batch_detail").html(ajax_load);
            $('#batch_buttons').hide();
            var form = $("form"); //Grab the form element from the DOM 
            //alert(form.serialize());
            var mydata = form.serialize();
            $.ajax({  
                type: "POST",  
                url: 'geo_getupdate_list.php', 
                data: mydata,  
                datatype: 'json',
                success: function(dat) {
                    alert('dat:'+ typeof dat ) //RETURNS STRING
                    //alert(dat.location[0].id_mdt); //RETURNS UNDEFINED
                    // Cache the batch_detail element
                    var $detail = $("#batch_detail").html('<label>Locations have been retrieved:<br>' + dat + '<label>');
                    $('#batch_buttons').show();
                    // Instead of several .append() calls on the same element, create a 
                    //   single string, and do one.
                    var appendString = '';
                    for(var key in dat) { alert(key); return false; };
                    /*for(i=0; i < count; i++){
                        appendString += 'display address: ' + data.location[i].displayaddr_mdt + 'flag: ' + data.location[i].flag_mdt;
                    }*/
                    $detail.append(appendString);
                }, 
                error: function(dat) { //Triggered if an error communicating with server   
                     //alert('fail');
                     $("#batch_detail").html('<label>There was an error: '+dat+'<label>');  
                     $('#batch_buttons').show();
                }
            });  
            return false; //Ignore the default behavior of the button click  
        }); 

the json that is returned is:

{"location":[{"id_mdt":"5","idetp_mdt":"1","name_mdt":null,"geoaddr_mdt":null,"displayaddr_mdt":"31a Arundel Gardens London W11 2LW","telephone_mdt":null,"email_mdt":null,"website_mdt":"http:\/\/","lat_mdt":"51.513561","lng_mdt":"-0.206519","active_mdt":"1","flag_mdt":"1","id_etp":"1","name_etp":"Stockist","icon_etp":null},{"id_mdt":"1","idetp_mdt":"1","name_mdt":null,"geoaddr_mdt":null,"displayaddr_mdt":"via todde 29 Ales Sardegna 09091","telephone_mdt":null,"email_mdt":null,"website_mdt":"http:\/\/","lat_mdt":"39.7670964","lng_mdt":"8.813689","active_mdt":"1","flag_mdt":"1","id_etp":"1","name_etp":"Stockist","icon_etp":null},{"id_mdt":"4","idetp_mdt":"1","name_mdt":null,"geoaddr_mdt":null,"displayaddr_mdt":"31a Arundel Gardens London W11 2LW","telephone_mdt":null,"email_mdt":null,"website_mdt":"http:\/\/","lat_mdt":"51.513561","lng_mdt":"-0.206519","ac开发者_如何学运维tive_mdt":"1","flag_mdt":"1","id_etp":"1","name_etp":"Stockist","icon_etp":null},{"id_mdt":"3","idetp_mdt":"1","name_mdt":null,"geoaddr_mdt":null,"displayaddr_mdt":"31a Arundel Gardens London W11 2LW","telephone_mdt":null,"email_mdt":null,"website_mdt":"http:\/\/","lat_mdt":"51.513561","lng_mdt":"-0.206519","active_mdt":"1","flag_mdt":"1","id_etp":"1","name_etp":"Stockist","icon_etp":null},{"id_mdt":"6","idetp_mdt":"1","name_mdt":null,"geoaddr_mdt":null,"displayaddr_mdt":"31a Arundel Gardens London W11 2LW","telephone_mdt":null,"email_mdt":null,"website_mdt":null,"lat_mdt":"51.513561","lng_mdt":"-0.206519","active_mdt":"1","flag_mdt":"1","id_etp":"1","name_etp":"Stockist","icon_etp":null},{"id_mdt":"7","idetp_mdt":"1","name_mdt":"Test","geoaddr_mdt":null,"displayaddr_mdt":"31a Arundel Gardens London W11 2LW","telephone_mdt":null,"email_mdt":null,"website_mdt":null,"lat_mdt":"51.513561","lng_mdt":"-0.206519","active_mdt":"1","flag_mdt":"1","id_etp":"1","name_etp":"Stockist","icon_etp":null}]}

how do i access the data in the array?

i have tried so many examples on here and other places and i cant get any to work. I think it may be to do with the returned json object it has [ symbols in it which i think is wrong?

the php i have to generate the json is as follows:

//have defined a recordset called $rs_locations
$rows = array();
while($r = mysql_fetch_assoc($rs_locations)) {
    $rows[] = $r;
}
$jsondata = json_encode($rows);
// trying to strip out the [ ] brackets but doesn't work
str_replace ("[", "", $jsondata);
str_replace ("]", "", $jsondata);
echo($jsondata);

any ideas anyone, i am so stuck, thanks

EDIT: Your dataType property is mis-spelled.

It should be dataType, not datatype.

Also, try changing the data parameter to some other name, like dat. I've seen problems with that before when your $.ajax() call has the data property set.

success: function( dat ) {
   // Then change all references from data to dat

Try this for your success: callback.

You were fetching the same #batch_detail element several times and continuously calling .append() on that element.

This way you cache a reference to the element, create a single String to append, and then do the append once after the loop is done.

The specific trouble you were having was that you needed to reference the Array stored at data.location directly.

 success: function(dat) {
     // Cache the batch_detail element
     var $detail = $("#batch_detail").html('<label>Locations have been retrieved:<br>' + dat + '<label>');
     $('#batch_buttons').show();
     var count = dat.location.length - 1;
       // Instead of several .append() calls on the same element, create a 
       //   single string, and do one.
     var appendString = '';
     for(i=0; i < count; i++){
         appendString += 'display address: ' + dat.location[i].displayaddr_mdt + 'flag: ' + dat.location[i].flag_mdt;
     }
     $detail.append( appendString );
 }, 

If I get your script right, you have to get the location array from data first:

var locations = data.location;
for(var location in locations) {
    console.debug(locations[location]);
}