index.js

var http = require('http');
var express = require('express');
var bodyParser = require('body-parser');
var KeenClient = require('keen-js');

// 1.) create an authenticated Keen analytics client
var keen = new KeenClient({
  projectId: 'your project ID here',
  writeKey: 'your write key here'
});

// 2.) Create an Express web application
var app = express();
app.use(bodyParser.urlencoded({ extended: false }));
app.set('view engine', 'ejs');

// 3.) Create an endpoint to handle incoming calls from Twilio
app.post('/call', function(request, response) {
  
  // 4.)  Send an event to Keen tracking the incoming call
  keen.addEvent('calls', {
    number: request.body.To, // The twilio number that got the call
    city: request.body.FromCity // the city the call came from
  }, function(error, apiResponse) {

    // 5.) Return TwiML to provide instructions for what to do during the
    // inbound call

    // First, set the response Content-Type to XML
    response.type('text/xml');

    // Then, decide what message to read back to the user. If the Keen API
    // request was successful, then read back a happy message. If not, read
    // a sad message :(
    if (error) {
      console.log(error);
      return response.render('twiml', { message: 'Sorry, an error happened.' });
    }
    response.render('twiml', { message: 'Your call has been recorded!' })
  });
});

// 6.) Start web application
var server = http.createServer(app);
server.listen(process.env.PORT || 3000, function() {
  console.log('Express server started.');
});

twiml.ejs

<Response>
  <Say voice="alice"><%= message %></Say>
</Response>