Build any realtime experience using Ably’s Pub/Sub JavaScript SDK. Supported on all popular platforms and frameworks, including Node, React, and Web Workers.
Ably Pub/Sub provides flexible APIs that deliver features such as pub-sub messaging, message history, presence, and push notifications. Utilizing Ably’s realtime messaging platform, applications benefit from its highly performant, reliable, and scalable infrastructure.
Ably LiveObjects is also available as a Pub/Sub JavaScript SDK plugin. You can use LiveObjects to synchronize application state across your clients at scale.
Find out more:
Everything you need to get started with Ably:
- Getting started with Pub/Sub in JavaScript
- Getting started with Pub/Sub in React
- Getting started with LiveObjects in JavaScript
Ably aims to support a wide range of platforms and browsers. If you experience any compatibility issues, open an issue in the repository or contact Ably support.
The following platforms are supported:
| Platform | Support |
|---|---|
| Node.js | >=16.x or later. See engines in package.json. |
| React | >=16.8.x |
| TypeScript | Type definitions are included in the package. |
| Webpack | Browser and server-side bundling supported. |
| Web Workers | Browser bundle and modular support. |
The following browser versions are supported:
| Browser | Version |
|---|---|
| Chrome | >=58 (April 19, 2017). |
| Firefox | >=52 (March 7, 2017). |
| Edge | >=79 (December 15, 2020). |
| Safari | >=11 (September 19, 2017). |
| Opera | >=45 (May 10, 2017). |
Note
Versions 1.2.x of the SDK support Internet Explorer >=9 and other older browsers, as well as Node.js >=8.17.
Important
SDK versions < 1.2.36 will be deprecated from November 1, 2025.
The Ably Pub/Sub SDK includes support for Webpack compiling browsers.
Webpack installation details
If you are using a version older than 1.2.5 you will need to add ably to externals in your Webpack config to exclude it from Webpack processing, and require and use it as an external module using require('ably') as above.
If you're compiling for the browser, Webpack will resolve ably from node_modules automatically when included in your package.json. You can then:
require('ably');
// or, for ES6/TypeScript:
import * as Ably from 'ably';With target: 'browser', Webpack uses the browser-compatible CommonJS build by default.
If needed, for example with custom targets:
-
Webpack 5: add an alias in your config:
alias: { ably: path.resolve(__dirname, 'node_modules/ably/build/ably.js'), }
-
Webpack < 5: directly import:
import * as Ably from 'ably/build/ably.js';
The Pub/Sub SDK has a modular (tree-shakable) variant to build with a small bundle sizes.
Modular variant details
Aimed at those who are concerned about their app's bundle size, the modular variant of the library allows you to create a client which has only the functionality that you choose. Unused functionality can then be tree-shaken by your module bundler.
The modular variant of the library provides:
- a
BaseRealtimeclass; - various plugins that add functionality to a
BaseRealtimeinstance, such asRest,RealtimePresence, etc.
To use this variant of the library, import the BaseRealtime class from ably/modular, along with the plugins that you wish to use. Then, pass these plugins to the BaseRealtime constructor as shown in the example below:
import { BaseRealtime, WebSocketTransport, FetchRequest, RealtimePresence } from 'ably/modular';
const client = new BaseRealtime({
key: 'YOUR_ABLY_API_KEY', // Replace with a real key from the Ably dashboard
plugins: {
WebSocketTransport,
FetchRequest,
RealtimePresence,
},
});You must provide:
- at least one HTTP request implementation; that is, one of
FetchRequestorXHRRequest; - at least one realtime transport implementation; that is, one of
WebSocketTransportorXHRPolling.
BaseRealtime offers the same API as the Realtime class described in the rest of this README. This means that you can develop an application using the default variant of the SDK and switch to the modular version when you wish to optimize your bundle size.
In order to further reduce bundle size, the modular variant of the SDK performs less logging than the default variant. It only logs:
- messages that have a
logLevelof 1 (that is, errors) - a small number of other network events
If you require more verbose logging, use the default variant of the SDK.
For more information view the TypeDoc references.
Read the CONTRIBUTING.md guidelines to contribute to Ably.
The CHANGELOG.md contains details of the latest releases for this SDK. You can also view all Ably releases on changelog.ably.com.
For help or technical support, visit Ably's support page.
Ably Pub/Sub works out-of-the-box in background scripts for Chrome extensions using manifest v2. However, since manifest v3 background pages are no longer supported, you will need to run Ably Pub/Sub JavaScript SDK inside a service worker.
If you are using this SDK in a service worker, note:
- In versions of Chrome before 116, active WebSockets would not reset the 30s service worker idle timer, resulting in the client being closed prematurely.
- In versions 116 and above, service workers will stay active as long as a client is connected.
To ensure compatibility, add the following to your manifest.json:
If you are using this SDK's realtime features, for example, WebSockets in a service worker, note:
- In versions of Chrome before 116, active WebSockets would not reset the 30s service worker idle timer, resulting in the client being closed prematurely.
- In versions 116 and above, service workers will stay active as long as a client is connected.
To ensure compatibility, add the following to your manifest.json:
{
// ...
"minimum_chrome_version": "116",
// ...
}If you're hitting a "connection limit exceeded" error and see rising connection counts in your Ably dashboard, it's likely due to multiple Ably.Realtime instances being created during development. Common causes:
Even for use client components, Next.js may execute them on the server during pre-rendering. This can create unintended Ably.Realtime connections from Node.js that remain open until you restart the development server.
Prevent server-side connections using autoConnect and a window check:
const client = new Ably.Realtime({
key: 'your-ably-api-key',
autoConnect: typeof window !== 'undefined',
});Creating the client inside React components can lead to a new connection on every render. To prevent this, move the new Ably.Realtime() call outside of component functions.
In development environments that use Hot Module Replacement (HMR), such as React, Vite, or Next.js, saving a file can recreate the Ably.Realtime client, while previous instances remain connected. Over time, this leads to a growing number of active connections with each code edit. To fix: Move the client to a separate file (e.g., ably-client.js) and import it. This ensures the client is recreated only when that file changes.
If you encounter a Failed to compile Module not found error or warnings related to keyv when using Ably Pub/Sub JavaScript SDK with Next.js, add ably to the serverComponentsExternalPackages list in next.config.js:
const nextConfig = {
// ...
experimental: {
serverComponentsExternalPackages: ['ably'],
},
};The issue is coming from the fact that when using App Router specifically, dependencies used inside Server Components and Route Handlers will automatically be bundled by Next.js. This causes issues with some packages, usually the ones that have complex require statements, for example, requiring some packages dynamically during runtime. keyv is one of those packages as it uses require statement dynamically when requiring its adapters (see code in repo):
keyv ends up being one of ably-js's upstream dependencies for the node.js bundle, which causes the errors above when using it with Next.js App Router.
Using serverComponentsExternalPackages opts out from using Next.js bundling for specific packages and uses native Node.js require instead.
This is a common problem in App Router for a number of packages (for example, see next.js issue vercel/next.js#52876), and using serverComponentsExternalPackages is the recommended approach here.
If you encounter an error such as connection limit exceeded during development, it may be caused by one of the following issues:
Use the autoConnect option to prevent the client from connecting when rendered on the server:
const client = new Ably.Realtime({ key: 'your-ably-api-key', autoConnect: typeof window !== 'undefined' });Avoid creating the client inside React components. Instead, move the client instantiation outside of the component to prevent it from being recreated on every render.
To avoid duplicate client instances caused by hot reloads, move the new Ably.Realtime() call into a separate file, for example, ably.js and export the client from there. This ensures a single shared instance is reused during development.