function (err, res) {
    if (err) return sender.emit('transmissionError', err, data.channelURI);
    sender.emit('transmitted', res, data.channelURI);
  }
function (err, res) {
    if (err) return sender.emit('transmissionError', err, data.channelURI);
    sender.emit('transmitted', res, data.channelURI);
  }
function ( err , res ) { if ( err ) return sender . emit ( 'transmissionError' , err , data . channelURI ) ; sender . emit ( 'transmitted' , res , data . channelURI ) ; }
called once done of is there was a transmission error
called once done of is there was a transmission error