const keyHandlers = {
  'ArrowDown': function (this: SomeComponent, $event) {
    // error on accessing private method.
    // `this` does not have method private `handleArrowDown`
    this.handleArrowDown($event);
  }
}

export class SomeComponent {
  onKeyDown($event) {
    if (typeof keyHandlers[$event.code] === 'function') {
      keyHandlers[$event.code].call(this, $event);
    }
  }
  private handleArrowDown(_event) {
    // ...
  }
}