Facebook Messenger Bot payload for basic text message replies from the Bot.

app.js

'use strict';

// Imports dependencies and set up http server
const PAGE_ACCESS_TOKEN = process.env.PAGE_ACCESS_TOKEN;

const
  express = require('express'),
  bodyParser = require('body-parser'),
  request = require('request'),
  app = express().use(bodyParser.json()); // creates express http server


// Sets server port and logs message on success
app.listen(process.env.PORT || 1337, () => console.log('webhook is listening'));

/// Accepts POST requests at /webhook endpoint
app.post('/webhook', (req, res) => {

  // Parse the request body from the POST
  let body = req.body;

  // Check the webhook event is from a Page subscription
  if (body.object === 'page') {

    body.entry.forEach(function(entry) {

      // Gets the body of the webhook event
      let webhook_event = entry.messaging[0];
      console.log(webhook_event);


      // Get the sender PSID
      let sender_psid = webhook_event.id;
      console.log('Sender ID: ' + sender_psid);

      // Check if the event is a message or postback and
      // pass the event to the appropriate handler function
      if (webhook_event.message) {
        handleMessage(sender_psid, webhook_event.message);
      } else if (webhook_event.postback) {

        handlePostback(sender_psid, webhook_event.postback);
      }

    });
    // Return a '200 OK' response to all events
    res.status(200).send('EVENT_RECEIVED');

  } else {
    // Return a '404 Not Found' if event is not from a page subscription
    res.sendStatus(404);
  }

});

//Landing Page
app.get('/', (req, res, next) => {
  res.status(200).json({
    message: "ChatBot!"
  })
});

// Adds support for GET requests to our webhook
app.get('/webhook', (req, res) => {

  // Your verify token. Should be a random string.
  let VERIFY_TOKEN = process.env.VERIFY_TOKEN;

  // Parse the query params
  let mode = req.query['hub.mode'];
  let token = req.query['hub.verify_token'];
  let challenge = req.query['hub.challenge'];

  // Checks if a token and mode is in the query string of the request
  if (mode && token) {

    // Checks the mode and token sent is correct
    if (mode === 'subscribe' && token === VERIFY_TOKEN) {

      // Responds with the challenge token from the request
      console.log('WEBHOOK_VERIFIED');
      res.status(200).send(challenge);

    } else {
      // Responds with '403 Forbidden' if verify tokens do not match
      res.sendStatus(403);
    }
  }
  // res.status(200).json({
  //   message: "successful GET requests"
  // })
});

// Handles messages events
function handleMessage(sender_psid, received_message) {
  let response;

 // Check if the message contains text
 if (received_message.text) {

   // Create the payload for a basic text message
   response = {
     "text": `You sent the message: ${received_message.text}!`
   }
 }

 // Sends the response message
 callSendAPI(sender_psid, response);
}

// Handles messaging_postbacks events
function handlePostback(sender_psid, received_postback) {

}

// Sends response messages via the Send API
function callSendAPI(sender_psid, response) {
  // Construct the message body
  let request_body = {
    "messaging_type": "RESPONSE",
    "recipient": {
      "id": sender_psid
    },
    "message": response
  }

  // Send the HTTP request to the Messenger Platform
  request({
    "uri": "https://graph.facebook.com/v2.6/me/messages",
    "qs": { "access_token": PAGE_ACCESS_TOKEN },
    "method": "POST",
    "json": request_body
  }, (err, res, body) => {
    if (!err) {
      console.log('message sent!')
    } else {
      console.error("Unable to send message:" + err);
    }
  });
}