Facebook messenger bot error “TypeError: Cannot read property '0' of undefined.”

Question

I'm trying to create a Facebook chatbot using NodeJS, Express, and a Heroku server.

I created my webhook on Heroku and had it verified and saved by Facebook. I then ran this code to connect my webhook to Facebook.

curl -ik -X POST "https://graph.facebook.com/v2.6/me/subscribed_apps?access_token=<token>"

this returned {success:true}.

So then I started adding code that would reply to incoming messages but I can't seem to get it to receive the sent information. Whenever I send a message I get no reply.

Everything is connected and running but this error I am getting "TypeError: Cannot read property '0' of undefined" is because I'm not getting the message information sent to my webhook from facebook. This is the line of code that is empty:

messaging_events = req.body.entry[0].messaging;

Here is my full code:

var express = require('express');
var bodyParser = require('body-parser');
var request = require("request")

var app = express();
var port = process.env.PORT || 3000;

// body parser middleware
app.use(bodyParser.urlencoded({ extended: true }));

app.get('/', function (req, res) {
  if (req.query['hub.verify_token'] === '8FKU9XWeSjnZN4ae') {
    res.send(req.query['hub.challenge']);
    console.log("app.get ran")
    res.sendStatus(200)
  }

  console.log("Error: wrong validation token")
})

app.post('/', function (req, res) {
  messaging_events = req.body.entry[0].messaging;
  console.log("app.post ran")
  for (i = 0; i < messaging_events.length; i++) {
    event = req.body.entry[0].messaging[i];
    sender = event.sender.id;
    if (event.message && event.message.text) {
      text = event.message.text;
      sendTextMessage(sender, "Text received, echo: "+ text.substring(0, 200));
    }
  }
  res.sendStatus(200);
});

app.listen(port, function () {
  console.log('Listening on port ' + port);
});

var token = "<myToken>";

function sendTextMessage(sender, text) {
  messageData = {
    text:text
  }
  request({
    url: 'https://graph.facebook.com/v2.6/me/messages',
    qs: {access_token:token},
    method: 'POST',
    json: {
      recipient: {id:sender},
      message: messageData,
    }
  }, function(error, response, body) {
    if (error) {
      console.log('Error sending message: ', error);
    } else if (response.body.error) {
      console.log('Error: ', response.body.error);
    }
  });
}

Here are my Heroku Logs:

So I'm confused as to why I'm not getting the message data when my webhook is connected to Facebook and they are communicating. I also made sure I had all the subscription fields necessary checked.

Anyone see the problem? Any help is appreciated. Thanks!

Edit: I'm following this guide by the way - https://developers.facebook.com/docs/messenger-platform/quickstart

Answer 1

I had the same problem. Can you add app.use(bodyParser.json()) before bodyParser.urlencoded() ) ?