code: function( aPortNumber )
          {
              var listener = zMIDI._listenerMap[ aPortNumber], inChannel;
  
              if ( listener )
              {
                  inChannel = zMIDI.getInChannels()[ aPortNumber ];
                  inChannel.close();
                  inChannel.removeEventListener( "midimessage", listener, true );
                  delete zMIDI._listenerMap[ aPortNumber ];
              }
          }
docs: detach a method to listen to MIDI message in events
  
  @public
  
  @param {number} aPortNumber index of the MIDI port stop listening on