This is the 13th in series of posts leading up Node.js Knockout, and covers using Tropo in your node app.

Tropo is a multi-channel communication platform that lets you build Phone, SMS and IM apps - all using the same Node.js codebase.

On the phone side, Tropo integrates with SIP (the industry standard for VoIP telephony) and Skype. On the SMS side, Tropo supports sending inbound and outbound text messages from both U.S. and Canadian numbers. (It’s also possible to send to a host of international destinations from U.S. numbers.)

Tropo is 100% free for development use - no upfront commitments and no strings attached. Signing up for an account is free, and you can deploy phone and SMS numbers for free in development (we have tons in both the US and Canada). We won’t ask you for payment information until you’re ready to deploy your application to production.

For Node.js developers, getting started using Tropo to build powerful communication apps is as simple as installing the Tropo Node.js module.

npm install tropo-webapi

Your Node.js application will interact with the Tropo platform by consuming and generating JSON that is delivered over HTTP. It’s simple to use a Node-based web server for this:

var TropoWebApi = require('tropo-webapi').TropoWebAPI;
var http = require('http');

var server = http.createServer(function (request, response) {

  var tropo = new TropoWebAPI();
  tropo.say("Hello, World!");
  response.writeHead(200, {'Content-Type': 'application/json'});


This simple web server listening on port 8000 will respond to incoming HTTP requests (Tropo uses the POST method to to connect to your app) with the following JSON:

{"tropo":[{ "say":{"value":"Hello, World!" }}]}

When a user makes a phone call to this app, Tropo to output the phrase “Hello, World” via Text-to-Speech (TTS) with the standard TTS engine. One of the really nice features is that we support TTS in multiple languages - 24 in all - so if your app has an international audience, Tropo is a logical fit.

Now lets look at a slightly more advanced example:

var TropoWebApi = require('tropo-webapi').TropoWebAPI;
var express = require('express');

var port = process.ARGV[2] || 8000;
var app = express.createServer();

// Required to process the body of HTTP responses from Tropo.

// Base route, plays welcome message.'/', function(req, res){
  var tropo = new TropoWebAPI();

  tropo.say("Welcome to the Tropo Web API node demo.");
  tropo.on("continue", null, "/start", true);


// Route to start asking caller for selection.'/start', function(req, res){

  var tropo = new TropoWebAPI();

  // Set up options for question to ask caller.
  var choices = new Choices("Node JS, PHP, Ruby, Python, Scala");
  var attempts = 3;
  var bargein = false;
  var minConfidence = null; // Use the platform default.
  var name = "test";
  var recognizer = "en-us";
  var required = true;
  var say = new Say("What is your favorite programming language?");
  var timeout = 5;
  var voice = "Allison";
  tropo.ask(choices, attempts, bargein, minConfidence, name, recognizer, required, say, timeout, voice);

  tropo.on("continue", null, "/answer", true);
  tropo.on("error", null, "/error", true);


// Route to handle valid answers.'/answer', function(req, res){

  var tropo = new TropoWebAPI();
  var selection = req.body['result']['actions']['value'];
  tropo.say('You chose, ' + selection + '. Thanks for playing.');


// Route to handle errors or invalid responses.'/error', function(req, res){

  var tropo = new TropoWebAPI();
  tropo.say("Whoops, something bad happened. Please try again later.");


console.log('Tropo demo running on port: ' + port);

Since interaction with the Tropo platform occurs via HTTP, Tropo apps are a great fit for the Express Framework. When you create your Tropo application, simply set the URL to this app - wherever it happens to be running - as the application start URL.

This sample application has 4 basic steps:

  • A welcome message.
  • An input collection segment, where the caller is asked to name their favorite programming language.
  • An input inspection segment, where the value of the caller’s input is simply read back to them.
  • An error handler to tell the user if an error occurs (always a good idea in phone applications).

At the end of each segment, JSON is rendered in the HTTP response and sent to Tropo. This rendered JSON is used to interact with the user on whatever channel they have chosen to connect to your application with.

You may notice the following code in the input collection segment:

var choices = new Choices("Node JS, PHP, Ruby, Python, Scala");

This is the list of choices that the user may select from - if the user calls your application, they will make their selection using their voice. One of the unique features of Tropo is the ability to support speech recognition. This functionality is available to all applications that need it at no additional cost.

When the user makes their selection, it is sent via HTTP POST to the input inspection segment, and read back to the caller. If the user happens to connect to your application via SMS or IM, the result will be delivered on those channels. That’s it! No additional code needed - Tropo apps are born to work on multiple channels.

Tropo’s unique features are perfect for simply building powerful, multi-channel applications that are fully interoperable with the latest telephony and communication standards.

Together, Tropo and Node.js are a knockout.

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