outgoing/button_postback.js
function buttonPostback(payload, callback)
{
  if (typeof payload.payload != 'string')
  {
    payload.payload = JSON.stringify(payload.payload);
  }

  callback(null, payload);
}
function buttonPostback(payload, callback)
{
  if (typeof payload.payload != 'string')
  {
    payload.payload = JSON.stringify(payload.payload);
  }

  callback(null, payload);
}
function buttonPostback ( payload , callback ) { if ( typeof payload . payload != 'string' ) { payload . payload = JSON . stringify ( payload . payload ) ; } callback ( null , payload ) ; }
Stringifies provided button.postback payload

@this  Fbbot#
@param {object} payload - button.postback object
@param {function} callback - invoked after stringification is done
Stringifies provided button . postback payload