Bidirectionality

The bidi package provides a common system for components to get and respond to change in the application's LTR/RTL layout direction.

link Directionality

When including the CDK's BidiModule, components can inject Directionality to get the current text direction (RTL or LTR);

link Example

@Component({ ... }) 
export class MyWidget implements OnDestroy {

  /** Whether the widget is in RTL mode or not. */
  private isRtl: boolean;

  /** Subscription to the Directionality change EventEmitter. */
  private _dirChangeSubscription = Subscription.EMPTY;  

  constructor(dir: Directionality) {
    this.isRtl = dir.value === 'rtl';

    _dirChangeSubscription = dir.change.subscribe(() => {
      this.flipDirection();
    });
  }

  ngOnDestroy() {
    this._dirChangeSubscription.unsubscribe();
  }
}  

link The Dir directive

The BidiModule also includes a directive that matches any elements with a dir attribute. This directive has the same API as Directionality and provides itself _as_ Directionality. By doing this, any component that injects Directionality will get the closest ancestor layout direction context.