Receiving H Events

What Are H Events?

H events, so named as they are prefixed with the text H:, are a new way of interacting with the simulator as of MSFS. They are defined in cockpit panel ModelBehaviors, and only go in one direction: from the panel to Javascript/HTML code.

H events are not required to be defined ahead of time, similar to L vars, and can be named with any contiguous alphanumeric characters. Each cockpit panel in MSFS sends a number of cockpit specific H events that have no analogous key event, such as pressing individual buttons on an FMS computer.

These individual panel specific events can be received by Javascript instruments.

How To Receive H Events

Inside your main instrument class that extends BaseInstrument, you must define the method onInteractionEvent() in order to receive H events:

class MyInstrument extends BaseInstrument {
  get templateID(): string {
    return 'MyInstrument';
  }

  //Will be called by the VCockpit system when a H event is received
  public onInteractionEvent(args: string[]): void {
    const hEventName = args[0];
    console.log(`Got a H Event named ${hEventName}!`);
  }
}

The avionics framework also provides a convenient utility publisher class to publish H events to an EventBus:

class MyInstrument extends BaseInstrument {
  private readonly eventBus = new EventBus();
  private readonly hEventPublisher = new HEventPublisher(this.eventBus);

  get templateID(): string {
    return 'MyInstrument';
  }

  public connectedCallback(): void {
    super.connectedCallback();
    this.hEventPublisher.startPublish();
  }

  public onInteractionEvent(args: string[]): void {
    this.hEventPublisher.dispatchHEvent(args[0]);
  }
}

//Later, in a component:
const subscriber = this.props.bus.getSubscriber<HEvent>();
subscriber.on('hEvent')
  .handle(eventName => console.log(`Got a H Event named ${eventName}!`));