Feature flags

Feature flags let you enable or disable functionality without deploying code. Use them to:

• Release features gradually
• Test in production with specific users
• Create kill switches for instant rollback
• Run A/B tests

Create a feature flag

1. Navigate to your project in the Replane dashboard
2. Click New Config
3. Enter the details:
   • Name: feature-dark-mode
   • Value: false
4. Click Create

Read the flag in your app

import { Replane } from '@replanejs/sdk'

const replane = new Replane()
await replane.connect({
  sdkKey: process.env.REPLANE_SDK_KEY!,
  baseUrl: 'https://replane.example.com'
})

if (replane.get('feature-dark-mode')) {
  enableDarkMode()
}

Enable for specific users

Add an override to enable the feature for beta testers:

1. Click on your config
2. Click Add Override
3. Configure:
   • Name: "Beta users"
   • Condition: userGroup equals beta
   • Value: true
4. Click Save

Now pass the context when reading:

const enabled = replane.get('feature-dark-mode', {
  context: { userGroup: user.group }
})

Beta users see true, everyone else sees false.

Enable for a percentage of users

For gradual rollouts, use percentage-based conditions:

1. Click Add Override
2. Configure:
   • Name: "10% rollout"
   • Condition: 10% of userId
   • Value: true
3. Click Save

const enabled = replane.get('feature-dark-mode', {
  context: { userId: user.id }
})

The same user always gets the same result (deterministic bucketing).

React to changes in realtime

Subscribe to flag changes:

replane.subscribe('feature-dark-mode', (config) => {
  if (config.value) {
    enableDarkMode()
  } else {
    disableDarkMode()
  }
})

Type-safe flags

Define your flag types:

interface Flags {
  'feature-dark-mode': boolean
  'feature-new-checkout': boolean
  'feature-ai-assistant': boolean
}

const replane = new Replane<Flags>({
  // Default values to use if the initial request to fetch configs fails.
  defaults: {
    'feature-dark-mode': false,
    'feature-new-checkout': true,
    'feature-ai-assistant': false
  }
})
await replane.connect({
  sdkKey: process.env.REPLANE_SDK_KEY!,
  baseUrl: 'https://replane.example.com'
})

// TypeScript knows this is a boolean
const darkMode = replane.get('feature-dark-mode')

Best practices

Naming conventions

Use a consistent prefix for feature flags:

feature-dark-mode
feature-new-checkout
feature-ai-recommendations

Clean up old flags

Remove flags after full rollout to avoid code clutter. Replane keeps version history, so you can always see what a flag was set to.

Use environments

Different values per environment:

Environment	Value	Use case
Production	false	Feature not yet released
Staging	true	Testing the feature
Development	true	Building the feature

Example: Kill switch

Create a kill switch to disable a feature instantly:

// Config: feature-payments-enabled, value: true

async function processPayment(order: Order) {
  if (!replane.get('feature-payments-enabled')) {
    throw new Error('Payments are temporarily disabled')
  }

  // Process payment...
}

If something goes wrong, set feature-payments-enabled to false in the dashboard. All instances update immediately via SSE.

Next steps

• Override Rules — Advanced targeting
• Gradual Rollouts — Percentage-based releases
• JavaScript SDK — Full API reference