JavaScript quickstart

Wire the browser SDK into your app and see your first flag fetch.

Wire the browser SDK into your app in three steps. This assumes you've already created a flag and copied a development SDK key — if not, start with the Quickstart.

1. Install

npm install switchbox-js

switchbox-js has zero runtime dependencies — it uses only the browser's fetch and Web Crypto APIs.

2. Create a client

Use the Switchbox.create() factory — it constructs the client and awaits the first config fetch, so the client is ready to evaluate as soon as it resolves. Create it once and reuse it.

import { Switchbox } from 'switchbox-js';


const client = await Switchbox.create({
  sdkKey: 'your-sdk-key-from-dashboard',
});

3. Check a flag

Evaluation is async (it uses Web Crypto for rollout hashing), so await it:

if (await client.enabled('new_checkout', { user_id: '42' })) {
  showNewCheckout();
} else {
  showOldCheckout();
}

The user object is optional — pass it when a flag uses targeting rules or a percentage rollout. After the first fetch, evaluation is a local lookup against the cached config; the SDK refreshes it in the background every 30 seconds.

When you're done (e.g. tearing down a session), stop the poller:

client.destroy();

See it connect

Load the page that creates the client. Within a few seconds, the development environment in the dashboard shows a Connected ✓ badge — your client is fetching its config from the edge.

Flip the flag in the dashboard and Save; the running page picks up the change on its next poll (within ~30 seconds).

Where to next