feature-flags

Feature Flags

Control feature releases and enable progressive rollout with feature flag systems.

When to Use This Skill

Use this skill when:

• Implementing gradual feature rollouts
• Enabling trunk-based development
• Running A/B tests and experiments
• Managing feature lifecycles
• Implementing kill switches for production

Prerequisites

• Application code access
• Feature flag service or self-hosted solution
• Basic understanding of deployment patterns

Feature Flag Types

Type	Purpose	Example
Release	Control feature visibility	New checkout flow
Experiment	A/B testing	Button color test
Ops	Runtime configuration	Rate limiting
Permission	User access control	Premium features
Kill Switch	Emergency disable	Third-party integration

LaunchDarkly

SDK Setup (Node.js)

const LaunchDarkly = require('launchdarkly-node-server-sdk');

const client = LaunchDarkly.init(process.env.LAUNCHDARKLY_SDK_KEY);

await client.waitForInitialization();

// Evaluate flag
const user = {
  key: 'user-123',
  email: '[email protected]',
  custom: {
    plan: 'premium',
    company: 'acme'
  }
};

const showNewFeature = await client.variation('new-checkout', user, false);

if (showNewFeature) {
  // New feature code
} else {
  // Existing code
}

React SDK

import { withLDProvider, useFlags, useLDClient } from 'launchdarkly-react-client-sdk';

// Provider setup
export default withLDProvider({
  clientSideID: 'your-client-side-id',
  user: {
    key: 'user-123',
    email: '[email protected]'
  }
})(App);

// Using flags in component
function FeatureComponent() {
  const { newCheckout, experimentVariant } = useFlags();
  const ldClient = useLDClient();

  // Track events
  const handleClick = () => {
    ldClient.track('checkout-started');
  };

  if (newCheckout) {
    return <NewCheckout onClick={handleClick} />;
  }
  return <OldCheckout onClick={handleClick} />;
}