Define a central feature flag configuration using a static file or dynamic API to manage feature states. 2. Create a reusable React hook like useFeatureFlag to easily access flag values across components, supporting both static and dynamic loading. 3. Use feature flags strategically for release toggles, A/B testing, user-based permissions, or kill switches, avoiding overuse. 4. Clean up old flags by setting expiration dates, tracking them centrally, and removing them once obsolete to prevent technical debt. Feature flags should be managed with discipline to maintain code clarity and ensure long-term maintainability.
Feature flags (also known as feature toggles) are a powerful technique that allows you to enable or disable functionality in your frontend application without deploying new code. They’re especially useful for gradual rollouts, A/B testing, and hiding incomplete features behind a flag during development.
Here’s how to implement feature flags effectively in a frontend application.
1. Define a Central Feature Flag Configuration
Start by creating a centralized configuration that defines which features are enabled. This can be a simple JavaScript object or loaded from an external source.
// features.js
const FEATURES = {
newCheckoutFlow: false,
darkMode: true,
userAnalyticsBeta: false,
};
export default FEATURES;For more flexibility, you can load flags from a backend API or config file:
// api/featureFlags.js
export async function getFeatureFlags() {
const response = await fetch('/api/feature-flags');
return response.json(); // e.g., { newCheckoutFlow: true, darkMode: false }
}This allows dynamic updates without redeploying the frontend.
2. Create a Feature Flag Hook or Utility
To make flags easy to use across components, create a reusable utility or React hook.
// hooks/useFeatureFlag.js
import { useEffect, useState } from 'react';
import getFeatureFlags from '../api/featureFlags';
const useFeatureFlag = (flagName) => {
const [isEnabled, setIsEnabled] = useState(false);
useEffect(() => {
getFeatureFlags().then((flags) => {
setIsEnabled(!!flags[flagName]);
});
}, [flagName]);
return isEnabled;
};
export default useFeatureFlag;Now you can use it in components:
function CheckoutButton() {
const isNewCheckoutEnabled = useFeatureFlag('newCheckoutFlow');
return isNewCheckoutEnabled ? <NewCheckout /> : <LegacyCheckout />;
}Tip: For static flags (defined at build time), you can skip async loading and use direct imports for better performance.
3. Use Feature Flags Strategically
Avoid overusing flags. They add complexity, so follow these patterns:
- Release Toggles: Short-lived flags for rolling out new features gradually.
- Experiment Toggles: Used for A/B testing different UI versions.
- Permission Toggles: Enable features based on user roles or plans.
- Kill Switches: Turn off problematic features quickly in production.
Example with user-based targeting:
const useFeatureFlag = (flagName, user) => {
const [isEnabled, setIsEnabled] = useState(false);
useEffect(() => {
getFeatureFlags().then((flags) => {
const flag = flags[flagName];
// Enable for internal users only
if (flag?.rollout === 'internal' && user.isInternal) {
setIsEnabled(true);
}
// Gradual rollout to 10% of users
else if (flag?.rollout === 'gradual') {
setIsEnabled(Math.random() < 0.1);
} else {
setIsEnabled(!!flag?.enabled);
}
});
}, [flagName, user]);
return isEnabled;
};4. Clean Up Old Flags
One of the biggest pitfalls is leaving old flags in the codebase. Make it a habit to:
- Set expiration dates on temporary flags.
- Track flags in a documentation file or dashboard.
- Remove flags once they’re no longer needed.
? Never leave a feature behind a flag forever. Either fully release it or remove the code.
Feature flags give you control and flexibility, but they should be managed carefully. With a clean setup and disciplined cleanup, they become a valuable tool in your frontend toolkit.
Basically: define flags, centralize access, use them wisely, and clean up often.
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