Answer by Warren Davis for AngularJS : Prevent error $digest already in progress when calling $scope.$apply()

Found this: https://coderwall.com/p/ngisma where Nathan Walker (near bottom of page) suggests a decorator in $rootScope to create func 'safeApply', code:

yourAwesomeModule.config([
  '$provide', function($provide) {
    return $provide.decorator('$rootScope', [
      '$delegate', function($delegate) {
        $delegate.safeApply = function(fn) {
          var phase = $delegate.$$phase;
          if (phase === "$apply" || phase === "$digest") {
            if (fn && typeof fn === 'function') {
              fn();
            }
          } else {
            $delegate.$apply(fn);
          }
        };
        return $delegate;
      }
    ]);
  }
]);