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How to Receive and Respond to Text Messages with Node.js, Express and Twilio

Screen Shot 2017-10-20 at 3.59.16 PM

You’re building an Express app and want to be able to respond to SMS messages? Let’s walk through how to add Twilio SMS to the Express “Hello World” app.

Installing dependencies

Before moving on, you’re going to need to have Node.js and npm installed. I am running version 8.6.0 and 5.3.0 respectively.

We’re going to use:

Navigate to the directory where you want this code to live and run the following command in your terminal to create an npm package for this project.

npm init --yes

The --yes just runs through all of the prompts that you would otherwise have to fill out or skip. Now that we have a package.json for our app, let’s install the necessary libraries:

npm install twilio@3.8.1 --save
npm install express@4.16.2 --save

The --save argument keeps track of the version of the library you installed in your package.json file.

Building a basic Express app

Let’s start with the code that the Express documentation uses for it’s “Hello World” example. Create and open a new file called index.js in your current directory and add the following code to it:

const express = require('express');
const MessagingResponse = require('twilio').twiml.MessagingResponse;

const app = express();

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Example app listening on port 3000!');
});

In this code, we are creating an app with Express and adding a route called / that takes GET requests. Whenever a GET request is sent to the default / route on our web app, a function is called that sends the string “Hello, World!” to the client. We are then having our app listen on port 3000 for any incoming requests.

Save the file and run the project with the terminal command node index in the same directory as package.json and index.js, then visit http://localhost:3000 to see “Hello, World.” on the screen.

Setting up your Twilio account

Before being able to respond to messages, you’ll need a Twilio phone number. You can buy a phone number here (it’s free if you’re using the number to test your code during development).

Your Express app will need to be visible from the Internet in order for Twilio to send requests to it. We will use ngrok for this, which you’ll need to install if you don’t have it. In your terminal run the following command:

ngrok http 3000

If you’ve just installed ngrok and that previous command didn’t work, you might have to run it like ./ngrok http 3000 from the directory that the ngrok executable is in.

Screen Shot 2017-10-20 at 3.45.06 PM.png

This provides us with a publicly accessible URL to the Flask app. Configure your phone number as seen in this image by adding your ngrok URL with /sms appended to it to the “Messaging” section:

Screen Shot 2017-10-20 at 3.45.41 PM.png

You are now ready to receive a text message to your new Twilio number.

Adding SMS to your Express app

Now that you have a Twilio number you want to allow users to send a text message to it and get a response.

We only need one route on this app: /sms to handle incoming text messages. Let’s add another route. Replace all of the code in index.js with the following:

const express = require('express');
const MessagingResponse = require('twilio').twiml.MessagingResponse;

const app = express();

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.post('/sms', (req, res) => {

  // Start our TwiML response.
  const twiml = new MessagingResponse();

  // Add a text message.
  const msg = twiml.message('Check out this sweet owl!');

  // Add a picture message.
  msg.media('https://demo.twilio.com/owl.png');

  res.writeHead(200, {'Content-Type': 'text/xml'});
  res.end(twiml.toString());
});

app.listen(3000, () => {
  console.log('Example app listening on port 3000!');
});

Run your code again:

node index.js

Now text your Twilio number and you should get a response!

What just happened?

With this app running on port 3000, sitting behind a public ngrok URL, Twilio can see your application. Upon receiving a text message:

  1. Twilio will send a POST request to /sms.
  2. The callback function associated with the /sms route will be called.
  3. This function responds to Twilio’s request with TwiML telling Twilio to send a message back in response (containing this sweet owl pic).

If you want to learn more thoroughly about Express and Twilio SMS check out the SMS and MMS Notifications tutorial or Appointment Reminders with Express.

Feel free to reach out if you have any questions or comments or just want to show off the cool stuff you’ve built.

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