Voice JavaScript SDK: Twilio in the browser

The Twilio Voice JavaScript SDK allows you to make voice calls to and from a web browser and a Twilio TwiML Voice Application. This means you can open inbound and outbound audio connections to Twilio for building softphones, walkie-talkies, conference calls, click-to-talk systems, and more, all from the browser.

You set up your device and establish a connection to Twilio. Audio from your device's microphone is sent to Twilio, and Twilio sends back audio which is played through your device's speakers, like on a normal phone call. The key difference is that with Twilio Voice JavaScript SDK, your "phone" is a Twilio.Device, a "soft device" that provides connections into Twilio.

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When you initiate a call using the Twilio.Device object provided by the JavaScript SDK, you're not calling another phone directly. Rather, you're connecting to Twilio and instructing Twilio to fetch TwiML from your server to handle the call. This is analogous to the way Twilio handles incoming calls from a real phone.

The JavaScript SDK uses the same TwiML verbs and nouns used for handling Twilio Voice calls. We've also added a new <Client> noun for dialing to a "client" (another instance of a Twilio.Device).

Because calls made with a Twilio.Device aren't made to a specific phone number, Twilio relies on a TwiML Application within your account to determine how to interact with your server. A TwiML Application is just a convenient way to store a set of URLs, like the VoiceUrl and SmsUrl on a phone number, but without locking them to a specific phone number. This makes TwiML Applications perfect for handling connections from your Twilio.Device — which is why we created them in the first place.

So when your Twilio.Device initiates a call to Twilio, a request is made to the VoiceUrl property of an Application within your account. You specify the Application you're connecting to with an Access Token. Twilio uses the TwiML response from its request to that Application's VoiceUrl to direct what happens with the Twilio.Device call.

We recommend using npm to add the Voice SDK as a dependency.

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npm install @twilio/voice-sdk --save
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Using this method, you can import the Voice SDK using ES Module or TypeScript syntax:

import { Device } from '@twilio/voice-sdk';

Or using CommonJS:

const Device = require('@twilio/voice-sdk').Device;

As of 2.0, the Twilio Voice SDK is no longer hosted via CDN.

Although we recommend using npm to add the Voice SDK as a dependency, you can also get the Twilio Voice SDK code from GitHub and include it in your project directly. To do so, navigate to "Releases" and find the most recent release, or the particular release version you'd like to use.

Download either the zip or the tar.gz and then extract the files. For example, if you downloaded the tarball for the 2.0.0 release, you could then extract the files with the tar command:

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tar -xvzf twilio-voice.js-2.0.0.tar.gz
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cd twilio-voice.js-2.0.0
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Once you've extracted the folder, the twilio.js and twilio.min.js files that you can include in your project will be in the /dist directory. twilio.min.js is the minified version of the code.

You can copy either the twilio.js or the twilio.min.js file into your project and then provide a link to it in your html. For example:

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<script type="text/javascript" src="twilio.min.js"></script>
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Using this method, you can access the SDK through the browser global:

const Device = Twilio.Device;

The following table indicates the browsers supported by the Twilio Voice JavaScript SDK. We support the most recent (N) and the two previous (N-2) versions of these browsers unless otherwise indicated.

* WebRTC support in Safari started with Safari version 11.

** We support Chromium-based Edge only. Legacy Edge isn't supported. See this advisory for more details.

Twilio Voice JavaScript SDK is also supported on the latest Electron version

As of version 1.3, Twilio Voice JavaScript SDK (formerly known as Twilio Client JS SDK) has been strictly following semantic versioning: minor-level updates only contain feature updates and are completely backward compatible with 1.3.0 and newer.

Support for twilio.js 1.1 and 1.2 ceased on February 14, 2018. If you are still using either of these versions, please use the Migration Guide to upgrade to the latest version.