$.ajax ({

  url: 'data.php?',
  type: 'GET',
  dataType: "json",
  success: function(data) {

  var clients = JSON.parse(data);

  for (var key in clients) document.write('Client:' + ' ' + key + '<br>');

  var key_list = Object.keys(clients);

  console.log(key_list.sort(clients));

  }

});