code: function (callback) {
                  doCheck(function (connectivity) {
                      if (connectivity.changed) {
                          $log.info('application is now ' + (connectivity.online ? 'online' : 'offline'));
                      }
                      if (typeof callback === 'function') {
                          callback(connectivity);
                      }
                  });
              }
docs: @ngdoc function
  @name w20CoreEnv.service:ConnectivityService#check
  @methodOf w20CoreEnv.service:ConnectivityService
  @param {Function} callback The function to be called after the connectivity check
  
  @description
  Explicitely check for application connectivity.