/onboardingv2

JavaScript (Browser) — SDK detail

• Official docs: JavaScript SDK reference
• API reference: Browser client (@launchdarkly/js-client-sdk)
• Recipe (detect / install): SDK Recipes (JavaScript Browser)

Use @launchdarkly/js-client-sdk: createClient, start(), then waitForInitialization({ timeout }). Always pass a timeout (the docs recommend 1–5 seconds); without one, connectivity issues can block your app. In v4, waitForInitialization always settles with a status (complete, failed, or timeout)—handle each path (Use promises to determine when the client is ready).

Client-side ID and env vars: Use the Client-side ID from Project settings > Environments (not a server SDK key). Bundler prefixes: Apply: environment configuration.

Use this in an ES module context that supports top-level await, or wrap in an async function.

Includes: Copy-paste onboarding sample below. After status === 'complete', replace the flush/log block with your own logic (the docs’ handleInitializedClient is only an illustration).

import { createClient } from '@launchdarkly/js-client-sdk';

const clientSideID = import.meta.env.VITE_LAUNCHDARKLY_CLIENT_SIDE_ID;

// A "context" is a data object representing users, devices, organizations, and
// other entities. You'll need this later, but you can ignore it for now.
const context = {
  kind: 'user',
  key: 'EXAMPLE_CONTEXT_KEY',
};

const client = createClient(clientSideID, context);
client.start();

const result = await client.waitForInitialization({ timeout: 5 });

if (result.status === 'complete') {
  await client.flush();
  console.log('SDK successfully initialized!');
} else if (result.status === 'failed') {
  console.error('LaunchDarkly initialization failed:', result.error);
} else if (result.status === 'timeout') {
  console.error(
    'LaunchDarkly initialization timed out; the client keeps retrying in the background.',
  );
}

For Create React App, replace import.meta.env.VITE_LAUNCHDARKLY_CLIENT_SIDE_ID with process.env.REACT_APP_LAUNCHDARKLY_CLIENT_SIDE_ID. For Next.js, use process.env.NEXT_PUBLIC_LAUNCHDARKLY_CLIENT_SIDE_ID.