sendTypingIndicator(recipientId, milliseconds) {
    const timeout = isNaN(milliseconds) ? 0 : milliseconds;
    if (milliseconds > 20000) {
      milliseconds = 20000;
      console.error('sendTypingIndicator: max milliseconds value is 20000 (20 seconds)');
    }
    return new Promise((resolve, reject) => {
      return this.sendAction(recipientId, 'typing_on').then(() => {
        setTimeout(() => this.sendAction(recipientId, 'typing_off').then((json) => resolve(json)), timeout);
      });
    });
  }
Convinient method to send a typing_on action and then a typing_off action after milliseconds to simulate the bot is actually typing. Max value is 20000 (20 seconds).
@param {Recipient|String} recipientId
@param {Number} milliseconds