How to model your entities - 9

Message.ts

// Message.ts
function fold<R>(
  onText: (message: TextMessage) => R,
  onImage: (message: ImageMessage) => R,
  onAudio: (message: AudioMessage) => R,
) => {
  return (message: Message): R => {
    switch (message.messageType) {
      case ‘TEXT’:
        return onText(message);

      case ‘IMAGE’:
        return onImage(message);

      case ‘AUDIO’:
        return onAudio(message);
    }
  }
}