Eagle Feature Toggle

A lightweight and flexible feature toggle system for Node.js applications.

Installation

npm install eagle-feature
# or
yarn add eagle-feature

Quick Start

import { initializeFeatureToggles, isFeatureEnabled } from 'eagle-feature';

// Initialize at application startup
await initializeFeatureToggles({
  environment: process.env.NODE_ENV
});

// Use in your application
if (isFeatureEnabled('newFeature')) {
  // Feature is enabled
}

Configuration

Create environment-specific feature toggle configurations in your project:

// src/features/environments/development.ts
import { Toggles } from 'eagle-feature';

const developmentToggles: Toggles = {
  newFeature: true,
  betaFeature: false,
  userSpecificFeature: (request) => {
    return request.user?.role === 'admin';
  }
};

export default developmentToggles;

Then initialize the feature toggles with your configuration path:

await initializeFeatureToggles({
  environment: process.env.NODE_ENV,
  configPath: './src/features/environments/development'
});

API Reference

initializeFeatureToggles(options: FeatureToggleOptions): Promise<void>

Initializes the feature toggle system with environment-specific configurations.

interface FeatureToggleOptions {
  environment: string;
  configPath?: string; // Optional custom path to your configuration
}

// Basic usage
await initializeFeatureToggles({
  environment: 'development'
});

// With custom configuration path
await initializeFeatureToggles({
  environment: 'development',
  configPath: './src/features/environments/development'
});

isFeatureEnabled(featureName: string, context?: any): boolean

Checks if a feature is enabled.

// Simple boolean toggle
isFeatureEnabled('newFeature');

// Context-aware toggle
isFeatureEnabled('userSpecificFeature', { user: { role: 'admin' } });

getFeatureToggles(): FeatureToggles

Returns the feature toggles instance.

const toggles = getFeatureToggles();

Feature Toggle Types

Boolean Toggles

{
  simpleFeature: true,
  disabledFeature: false
}

Function Toggles

{
  userSpecificFeature: (request) => {
    return request.user?.role === 'admin';
  },
  timeBasedFeature: (request) => {
    return new Date().getHours() > 12;
  }
}

Error Handling

The system will throw errors in the following cases:

• When trying to use feature toggles before initialization
• When there's an error loading the environment configuration
• When a feature toggle function throws an error (returns false by default)

Best Practices

1. Initialize feature toggles at application startup
2. Keep your feature toggle configurations in your project's source code
3. Use environment-specific configurations
4. Keep feature toggle names descriptive and consistent
5. Use TypeScript for better type safety
6. Handle errors appropriately in your application

Example Usage with Express

import express from 'express';
import { initializeFeatureToggles, isFeatureEnabled } from 'eagle-feature';

const app = express();

// Initialize feature toggles
await initializeFeatureToggles({
  environment: process.env.NODE_ENV,
  configPath: './src/features/environments/development'
});

app.get('/api/feature', (req, res) => {
  if (isFeatureEnabled('newFeature', req)) {
    res.json({ message: 'New feature is enabled' });
  } else {
    res.json({ message: 'Feature is disabled' });
  }
});

License

MIT