_isActive(routerState /* RouterState */) {
    if (this.loading) {
      return false;
    }
    let currentWhen = this['current-when'];
    if (typeof currentWhen === 'boolean') {
      return currentWhen;
    }
    let { _models: models, _routing: routing } = this;
    if (typeof currentWhen === 'string') {
      return currentWhen
        .split(' ')
        .some((route) =>
          routing.isActiveForRoute(
            models,
            undefined,
            this._namespaceRoute(route),
            routerState,
          ),
        );
    } else {
      return routing.isActiveForRoute(
        models,
        this._query,
        this._route,
        routerState,
      );
    }
  }
Accessed as a classname binding to apply the component's `activeClass`
      CSS `class` to the element when the link is active.
  
      This component is considered active when its `currentWhen` property is `true`
      or the application's current route is the route this component would trigger
      transitions into.
  
      The `currentWhen` property can match against multiple routes by separating
      route names using the ` ` (space) character.
  
      @property active
      @private