code: function (pres)
      {
          if (this.socket && this.socket.readyState !== WebSocket.CLOSED) {
              if (pres) {
                  this._conn.send(pres);
              }
              var close = $build("close", { "xmlns": Strophe.NS.FRAMING, });
              this._conn.xmlOutput(close);
              var closeString = Strophe.serialize(close);
              this._conn.rawOutput(closeString);
              try {
                  this.socket.send(closeString);
              } catch (e) {
                  Strophe.info("Couldn't send <close /> tag.");
              }
          }
          this._conn._doDisconnect();
      }
docs: PrivateFunction: _disconnect
  _Private_ function called by Strophe.Connection.disconnect
  
  Disconnects and sends a last stanza if one is given
  
  Parameters:
  (Request) pres - This stanza will be sent before disconnecting.