Dialogflow + Facebook Messenger: handle stickers and images (node.js)

server.js

/*
some code...
*/
function imagesFunc(agent) {
  const sticker_id = agent.request_.body.originalDetectIntentRequest.payload.data.message.sticker_id; // get "sticker_id"
  if (sticker_id != undefined) { // it's a sticker
   agent.add("That is nice sticker!"); // send answer to user
   } else { // it is not a sticker
   agent.add("Thank you for image!"); // send answer to user
   }
}
/*
more code....
*/
intentMap.set('images', imagesFunc) // ("name Of Intent", functionName)