Feature Flag SDK

A flexible and extensible feature flag SDK that supports multiple providers and caching.

Features

• Support for multiple feature flag providers (Amplitude, Flagsmith)
• In-memory caching with customizable TTL
• TypeScript support
• Easy to extend with new providers

Basic Usage

The SDK provides four main functions for interacting with feature flags:

• isFeatureEnabled - Check if a feature is enabled (cached)
• getFeatureValue - Get the value of a feature flag (cached)
• isFeatureEnabledLatest - Check if a feature is enabled (real-time)
• getFeatureValueLatest - Get the value of a feature flag (real-time)

import {
  isFeatureEnabled,
  getFeatureValue,
  isFeatureEnabledLatest,
  getFeatureValueLatest,
} from '@rudderlabs/rudder-service';

// Using cached functions (recommended for most use cases)
async function processEvent(event) {
  const isEnabled = await isFeatureEnabled('tenantId', 'myFeature');
  if (isEnabled) {
    // process event
  }
}

// Using latest functions (for startup or critical real-time updates)
async function start() {
  // Get fresh values during startup
  const features = await Promise.all([
    getFeatureValueLatest('tenantId', 'routing'),
    getFeatureValueLatest('tenantId', 'theme'),
  ]);
  // Initialize app with latest values and start
}

Cached vs Latest Functions

Cached Functions (isFeatureEnabled, getFeatureValue)

Recommended for:

• Regular feature checks during runtime
• Feature checks while processing events
• Frequent feature flag queries
• Performance-critical operations

Benefits:

• Faster response times
• Lower latency
• Reduced server load
• Better user experience

Latest Functions (isFeatureEnabledLatest, getFeatureValueLatest)

Best for:

• Application startup configuration
• Features that need guaranteed latest values
• One-time initialization
• Critical business logic requiring real-time values

Note: These functions make direct calls to the feature flag provider and may have higher latency. Use them sparingly and only when necessary.

Best Practices

1. Default to Cached Functions

   // Preferred for most scenarios
   const isEnabled = await isFeatureEnabled('tenantId', 'feature');

2. Use Latest Functions at Startup

   // Good for initialization
   async function initializeApp() {
     const config = await getFeatureValueLatest('tenantId', 'appConfig');
     // Setup app with latest configuration
   }

3. Error Handling

   try {
     const isEnabled = await isFeatureEnabled('tenantId', 'feature');
   } catch (error) {
     // Handle error appropriately
     console.error('Failed to check feature:', error);
   }

When to Use Latest Functions

1. Application Initialization

   async function startupConfig() {
     // Get fresh values during startup
     const features = await Promise.all([
       getFeatureValueLatest('tenantId', 'routing'),
       getFeatureValueLatest('tenantId', 'theme'),
     ]);
     // Initialize app with latest values
   }

2. Critical Business Features

   async function processPayment() {
     // Check latest feature state for critical operations
     const paymentConfig = await getFeatureValueLatest('tenantId', 'paymentProcessing');
     // Process payment using latest configuration
   }

Remember: While latest functions provide real-time values, they come with additional latency and server load. Use them judiciously and prefer cached functions for regular operations.