A browser client that can be used together with the unleash-proxy.

Usage no npm install needed!

<script type="module">
  import anttiviljamiUnleashProxyClient from 'https://cdn.skypack.dev/@anttiviljami/unleash-proxy-client';


Unleash Proxy Client for the browser (js)

This is a tiny Unleash Client SDK you can use together with the Unleash Proxy. This makes it super simple to use Unleash from any single page app.

This client expect fetch to be available. If you need to support older browsers you should probably use the fetch polyfill.

Frameworks supported

This package is not tied to any framework, but can be used together most popular frameworks, examples:

How to use the client as a module.

Step 1: Install

npm install unleash-proxy-client --save

Step 2: Initialize the SDK You need to have a Unleash-hosted instance, and the proxy need to be enabled. In addition you will need a proxy-specific clientKey in order to connect to the Unleash-hosted Proxy.

import { UnleashClient } from 'unleash-proxy-client';

const unleash = new UnleashClient({
    url: 'https://eu.unleash-hosted.com/hosted/proxy',
    clientKey: 'your-proxy-key',
    appName: 'my-webapp'

// Used to set the context fields, shared with the Unleash Proxy
unleash.updateContext({userId: '1233'});

// Start the background polling

Step 3: Check if feature toggle is enabled


Step 4: Get toggle variant

const variant = unleash.getVariant('proxy.demo');
if(variant.name === 'blue') {
 // something with variant blue...

Listen for updates via the EventEmitter The client is also an event emitter. This means that your code can subscribe to updates from the client. This is a neat way to update a single page app when toggle state updates.

unleash.on('update', () => {
    const myToggle = unleash.isEnabled('proxy.demo');
    //do something useful

SessionId - Important note!

You may provide a custom session id via the "context". If you do not provide a sessionId this SDK will create a random session id, which will also be stored in the provided storage (local storage). By always having a consistent sessionId available ensures that even "anonymous" users will get a consistent experience when feature toggles is evaluated, in combination with a gradual (percentage based) rollout.

Custom store

This SDK will use @react-native-async-storage/async-storage to backup feature toggles locally. This is useful for bootstrapping the SDK the next time the user comes back to your application.

You can provide your own storage implementation.


import SharedPreferences from 'react-native-shared-preferences';
import { UnleashClient } from 'unleash-proxy-client';

const unleash = new UnleashClient({
    url: 'https://eu.unleash-hosted.com/hosted/proxy',
    clientKey: 'your-proxy-key',
    appName: 'my-webapp',
    storage: {
        save: (name: string, data: any) => SharedPreferences.setItem(name, data),
        get: (name: string) => SharedPreferences.getItem(name, (val) => val)

How to use the client via CDN.

    <script src="https://unpkg.com/unleash-proxy-client@latest/build/main.min.js" type="text/javascript"></script>
    <script type="text/javascript">
        var config = {url: 'https://app.unleash-hosted.com/demo/proxy', clientKey: 'proxy-123', appName: 'web'};
        var client = new unleash.UnleashClient(config);
        client.updateContext({userId: '1233'})

        client.on('update', () => {