jquery ajax request with json response

$.ajax({
                        type:'POST',
                        url:'http://mysite.com/url',
                        data:{fieldname: 'fieldvalue'},
                        dataType: "json",
                        success: function(data , status, xhr) {
                              alert('ajax request successful');

                        }, fail:function(data){

                                alert('ajax request failed');
                        }
 });