Facebook Messenger Bot - Handle postback payload

index.js

const Facebook = require('Facebook');
exports.handler = (event, context, callback) => {
  /* ... 
  Get messaging event // see https://gist.github.com/alexandrenicol/f01f867cb175cd89e3e100c508cc6f4a#file-index-js
  ... */
      // Iterate over each messaging event
      entry.messaging.forEach(function(event) {
        if (event.message) {
          const message = event.message.text;
          const senderID = event.sender.id;
          Facebook.sendTextMessage(senderID, `you said: ${message}`);   
        } else if (event.postback) {
          if (event.postback.payload === 'get_started'){
            Facebook.sendTextMessage(event.sender.id, `Welcome to the Weather station Bot`);
          } else if (event.postback.payload === 'help'){
            Facebook.sendTextMessage(event.sender.id, `You can ask for the current temperature or humidity, either for your indoor or outdoor module`);
          } else {
            console.log("Webhook received unknown event: ", event);
          }
        } else {
          console.log("Webhook received unknown event: ", event);
        }
      });
    });
  /*...
  some code // see https://gist.github.com/alexandrenicol/f01f867cb175cd89e3e100c508cc6f4a#file-index-js
  ... */
}