code: function subscribeToEvents() {
      const socket = _socket.get(this);
  
      function onEventApiError(error) {
          dbg('Event API connection error: ' + JSON.stringify(error));
      }
  
      socket.on('pong', (latency) => {
          dbg(`Event API latency: ${latency} ms`);
      });
      socket.on('connect_error', onEventApiError);
      socket.on('error', onEventApiError);
      socket.on('disconnect', onEventApiError);
      socket.on('reconnect_error', onEventApiError);
      socket.on('reconnect_failed', () => {
          onEventApiError('Reconnecting to the Event API failed');
      });
  
      socket.on('new_receipt', receiptJSON => {
          const receipt = Receipt.from(receiptJSON, _provider.get(this));
          _eventEmitter.get(this).emit(EventNames.newReceipt, receipt);
      });
  }
docs: Subscribes to critical socket.io events and relays nahmii events to any
  registered listeners.
  Private method, invoke with 'this' bound to provider instance.
  @private