code: function (url, parameterName, callback) {
  
                  // Generate a unique function name for the JSONP callback.
                  var functionName = "gov_nasa_worldwind_jsonp_" + WWUtil.jsonpCounter++;
  
                  // Define a JSONP callback function. Assign it to global scope the browser can find it.
                  window[functionName] = function (jsonData) {
                      // Remove the JSONP callback from global scope.
                      delete window[functionName];
  
                      // Call the client's callback function.
                      callback(jsonData);
                  };
  
                  // Append the callback query parameter to the URL.
                  var jsonpUrl = url + (url.indexOf('?') === -1 ? '?' : '&');
                  jsonpUrl += parameterName + "=" + functionName;
  
                  // Create a script element for the browser to invoke.
                  var script = document.createElement('script');
                  script.async = true;
                  script.src = jsonpUrl;
  
                  // Prepare to add the script to the document's head.
                  var head = document.getElementsByTagName('head')[0];
  
                  // Set up to remove the script element once it's invoked.
                  var cleanup = function () {
                      script.onload = undefined;
                      script.onerror = undefined;
                      head.removeChild(script);
                  };
  
                  script.onload = cleanup;
                  script.onerror = cleanup;
  
                  // Add the script element to the document, causing the browser to invoke it.
                  head.appendChild(script);
              }
docs: Request a resource using JSONP.
  @param {String} url The url to receive the request.
  @param {String} parameterName The JSONP callback function key required by the server. Typically
  "jsonp" or "callback".
  @param {Function} callback The function to invoke when the request succeeds. The function receives
  one argument, the JSON payload of the JSONP request.