code: function jsonp(options, successCallback, errorCallback) {
      /*jshint camelcase:false */
  
      options = options || {};
  
      // Define unique callback name.
      var uniqueName = 'callback_json' + (++counter);
  
      // Send all data (including method, api key and data) via GET
      // request params.
      var params = options.params || {};
      params.callback = uniqueName;
      params.access_token = options.authorization;
      params.method = options.method || 'get';
      params.data = JSON.stringify(options.data);
      options.params = params;
  
      options.apiUrl = options.apiUrl && options.apiUrl.replace('//api', '//js-api');
  
      // Evrythng REST API default endpoint does not provide JSON-P
      // support, which '//js-api.evrythng.com' does.
      var url = Utils.buildUrl(options);
  
      // Return a promise and resolve/reject it in the callback function.
      return new Promise(function(resolve, reject) {
  
        // Attach callback as a global method. Evrythng's REST API error
        // responses always have a status and array of errors.
        window[uniqueName] = function(response){
  
          if (response.errors && response.status) {
  
            var errorData = _buildError(url, response.status, params.method, response);
            Logger.error(errorData);
  
            if(errorCallback) {
              Logger.warnCallbackDeprecation();
              errorCallback(errorData);
            }
            reject(errorData);
  
          }else {
  
            if(successCallback) {
              Logger.warnCallbackDeprecation();
              successCallback(response);
            }
  
            try {
              response = JSON.parse(response);
            } catch(e){}
  
            resolve(response);
          }
  
          // Remove callback from window.
          try {
            delete window[uniqueName];
          } catch (e) {}
          window[uniqueName] = null;
        };
  
        _load(url, reject);
  
      });
    }
docs: Jsonp method sets prepares the script url with all the information provided and defines the callback handler.