stf-DeviceFarmer/res/app/components/stf/page-visibility/page-visibility-directive.js

module.exports = function pageVisibilityDirective($document, $rootScope) {
  return {
    restrict: 'A',
    link: function (scope) {
      function pageVisibilityChanged() {
        if (document.hidden) {
          $rootScope.$broadcast('pageHidden')
        } else {
          $rootScope.$broadcast('pageVisible')
          // Application is visible to the user
          // Adjust polling rates and display update for active display mode
        }
      }

      document.addEventListener(
        'visibilitychange'
      , pageVisibilityChanged
      , false
      )

      scope.$on('$destroy', function () {
        angular.element(document).unbind('visibilitychange');
      })
    }
  }
}