this.hubConnection
  .start()
  .then(() => console.log('Connection started!'))
  .catch(err => console.log('Error while establishing connection :('));

this.hubConnection.on('ReceiveMessage', (userId: string, message: string) => {
    const text = `${userId}: ${message}`;
    this.messages.push(text);
  });

this.hubConnection
  .invoke('SendMessage', 'john', 'hello world')
  .catch(err => console.error(err));