JavaScript SDK API Reference

Complete API documentation for the JavaScript/TypeScript SDK.

new Replane<T>(options?)

Creates a new Replane client instance. The client is usable immediately if you provide defaults or a snapshot.

Constructor Options

Option	Type	Required	Description
defaults	Record<string, unknown>	No	Default values to use before connecting
context	Record<string, unknown>	No	Default context for all override evaluations
snapshot	ReplaneSnapshot<T>	No	Restore from a previous getSnapshot() call
logger	Logger	No	Custom logger (default: console)

replane.connect(options)

Connects to the Replane server and starts receiving real-time updates via SSE. Returns a Promise that resolves when the connection is established.

Connect Options

Option	Type	Required	Description
sdkKey	string	Yes	SDK key for authentication
baseUrl	string	Yes	Replane server URL
fetchFn	typeof fetch	No	Custom fetch implementation
requestTimeoutMs	number	No	SSE request timeout (default: 2000)
connectTimeoutMs	number	No	Connection timeout (default: 5000)
retryDelayMs	number	No	Delay between retries (default: 200)
inactivityTimeoutMs	number	No	SSE inactivity timeout (default: 30000)
agent	string	No	Agent identifier for User-Agent header

Example

const replane = new Replane<Configs>({
  defaults: {
    'feature-flag': false,
    'rate-limit': 100
  },
  context: {
    env: 'production',
    region: 'us-east'
  }
})

await replane.connect({
  sdkKey: process.env.REPLANE_SDK_KEY,
  baseUrl: 'https://replane.example.com',
  requestTimeoutMs: 5000,
  connectTimeoutMs: 10000
})

replane.get<K>(name, options?)

Gets a config value. Returns the current value synchronously.

Parameters

Parameter	Type	Required	Description
name	keyof T	Yes	Config name
options.context	Record<string, string | number | boolean | null | undefined>	No	Context for override evaluation
options.default	T[K]	No	Default value to return if config not found (prevents throwing)

Returns

The config value with type T[K], or the default value if provided and config is not found.

Example

// Simple get
const enabled = replane.get('feature-dark-mode') // boolean

// With context
const limit = replane.get('api-rate-limit', {
  context: { plan: 'premium' }
}) // number

// With default value - won't throw if config doesn't exist
const timeout = replane.get('timeout-ms', { default: 5000 }) // number

replane.subscribe(name, callback)

Subscribes to a specific config's changes. Returns an unsubscribe function.

const unsubscribe = replane.subscribe('feature-flag', (config) => {
  console.log('Feature flag changed:', config.value)
  // config.value is typed based on your Configs interface
})

// Later: stop receiving updates
unsubscribe()

replane.disconnect()

Disconnects from the server and cleans up resources. Safe to call multiple times. Call this when shutting down your application.

process.on('SIGTERM', () => {
  replane.disconnect()
  process.exit(0)
})

replane.getSnapshot()

Returns a serializable snapshot of the current config state. Use for SSR hydration or persisting state.

const snapshot = replane.getSnapshot()

// Later, restore from snapshot
const newClient = new Replane({ snapshot })