Method subscribe

web/src/tracker/connection.ts:99–103

(fn: Listener)

  }

  subscribe(fn: Listener): () => void {
    this.listeners.add(fn);
    fn(this.stream);
    return () => this.listeners.delete(fn);
  }

  private update(partial: Partial<TrackerStreamState>): void {
    this.stream = { ...this.stream, ...partial };