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Version: 2.0.0

Node.js SDK

Get your Featureflow account at featureflow.io

GitHub: https://github.com/featureflow/featureflow-node-sdk

Installation​

npm install --save featureflow-node-sdk

Quick Start​

Create a Featureflow Client​

Require the SDK and create a client with your Server Environment API Key:

const Featureflow = require('featureflow-node-sdk');

const featureflow = new Featureflow.Client({
  apiKey: 'sdk-srv-env-YOUR_API_KEY'
});

Or using ES6 imports:

import Featureflow from 'featureflow-node-sdk';

const featureflow = new Featureflow.Client({
  apiKey: 'sdk-srv-env-YOUR_API_KEY'
});
Singleton Pattern

The featureflow client should be instantiated once and shared across your application. Do not create a new client for each request.

Waiting for Ready State​

The client loads feature rules asynchronously. Use the callback or ready() method to ensure features are available:

// Option 1: Callback
new Featureflow.Client({ apiKey: 'YOUR_API_KEY' }, function(error, featureflow) {
  // featureflow is ready to use
});

// Option 2: Ready method
const featureflow = new Featureflow.Client({ apiKey: 'YOUR_API_KEY' });

featureflow.ready(function() {
  // featureflow is ready to use
});

Evaluate a Feature​

Check the value of a feature flag:

if (featureflow.evaluate('my-feature-key', user).isOn()) {
  // Feature is enabled
}

if (featureflow.evaluate('my-feature-key', user).isOff()) {
  // Feature is disabled
}

For custom variants:

if (featureflow.evaluate('my-feature-key', user).is('red')) {
  console.log('Showing red variant');
}

User Targeting​

Define users to target features to specific segments:

const user = new Featureflow.UserBuilder('unique-user-id')
  .withAttribute('country', 'US')
  .withAttribute('tier', 'gold')
  .withAttributes('roles', ['USER_ADMIN', 'BETA_CUSTOMER'])
  .build();

featureflow.evaluate('my-feature', user).isOn();

For simple cases, you can pass just the user ID:

featureflow.evaluate('my-feature', 'user-123').isOn();

Pre-registering Features​

Define default variants for features that may not yet exist in Featureflow. These serve as failover values when the server is unreachable:

const featureflow = new Featureflow.Client({
  apiKey: 'YOUR_API_KEY',
  withFeatures: [
    new Featureflow.Feature('feature-one', 'on').build(),
    new Featureflow.Feature('feature-two').build(),        // defaults to 'off'
    new Featureflow.Feature('feature-three', 'custom').build()
  ]
});

Environment Variable​

You can set your API key via environment variable instead of passing it directly:

export FEATUREFLOW_SERVER_KEY=sdk-srv-env-YOUR_API_KEY
// No apiKey needed when env var is set
const featureflow = new Featureflow.Client();

Express Integration​

For Express applications, initialize the client once at startup:

const express = require('express');
const Featureflow = require('featureflow-node-sdk');

const app = express();

const featureflow = new Featureflow.Client({
  apiKey: 'sdk-srv-env-YOUR_API_KEY'
});

featureflow.ready(() => {
  app.get('/', (req, res) => {
    const user = new Featureflow.UserBuilder(req.user.id)
      .withAttribute('plan', req.user.plan)
      .build();

    if (featureflow.evaluate('new-homepage', user).isOn()) {
      res.render('homepage-new');
    } else {
      res.render('homepage');
    }
  });

  app.listen(3000);
});

See the full Express example on GitHub.

API Reference​

Evaluate Methods​

MethodDescription
evaluate(featureKey, user).isOn()Returns true if variant equals "on"
evaluate(featureKey, user).isOff()Returns true if variant equals "off"
evaluate(featureKey, user).is(value)Returns true if variant equals the specified value
evaluate(featureKey, user).value()Returns the current variant value as a string

UserBuilder Methods​

MethodDescription
withAttribute(key, value)Add a single attribute
withAttributes(key, array)Add an array attribute
build()Build the user object

Next Steps​

License​

Apache-2.0