JavaScript Feature Flags

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Overview

This page describes how to instrument your browser JavaScript application with the Datadog Feature Flags SDK. Datadog feature flags provide a unified way to remotely control feature availability in your app, experiment safely, and deliver new experiences with confidence.

The Datadog Feature Flags SDK for JavaScript is built on OpenFeature, an open standard for feature flag management. This guide explains how to install the SDK, configure the Datadog provider, and evaluate flags in your application.

Installation

Install the Datadog OpenFeature provider and the OpenFeature Web SDK using your preferred package manager:

npm install @datadog/openfeature-browser @openfeature/web-sdk @openfeature/core

yarn add @datadog/openfeature-browser @openfeature/web-sdk @openfeature/core

pnpm add @datadog/openfeature-browser @openfeature/web-sdk @openfeature/core

Initialize the provider

Create a DatadogProvider instance with your Datadog credentials:

import { DatadogProvider } from '@datadog/openfeature-browser';
import { OpenFeature } from '@openfeature/web-sdk';

const provider = new DatadogProvider({
  applicationId: '<APPLICATION_ID>',
  clientToken: '<CLIENT_TOKEN>',
  env: '<ENV_NAME>',
});

Set the evaluation context

Define who or what the flag evaluation applies to using an evaluation context. The evaluation context includes user or session information used to determine which flag variations should be returned. Reference these attributes in your targeting rules to control who sees each variant.

const evaluationContext = {
  targetingKey: 'user-123',
  user_id: '123',
  user_role: 'admin',
  email: 'user@example.com',
};

await OpenFeature.setProviderAndWait(provider, evaluationContext);

The targetingKey is used as the randomization subject for percentage-based targeting. When a flag targets a percentage of subjects (for example, 50%), the targetingKey determines which "bucket" a user falls into. Users with the same targetingKey always receive the same variant for a given flag.

Evaluate flags

After the provider is initialized, you can evaluate flags anywhere in your application. Flag evaluation is local and instantaneous—the SDK uses locally cached data, so no network requests occur when evaluating flags.

Get a client

Retrieve the OpenFeature client to evaluate flags:

const client = OpenFeature.getClient();

Boolean flags

Use getBooleanValue(key, defaultValue) for flags that represent on/off or true/false conditions:

const isNewCheckoutEnabled = client.getBooleanValue('checkout_new', false);

if (isNewCheckoutEnabled) {
  showNewCheckoutFlow();
} else {
  showLegacyCheckout();
}

String flags

Use getStringValue(key, defaultValue) for flags that select between multiple variants or configuration strings:

const theme = client.getStringValue('ui_theme', 'light');

switch (theme) {
  case 'dark':
    setDarkTheme();
    break;
  case 'light':
  default:
    setLightTheme();
}

Number flags

Use getNumberValue(key, defaultValue) for numeric flags such as limits, percentages, or multipliers:

const maxItems = client.getNumberValue('cart_items_max', 20);
const priceMultiplier = client.getNumberValue('pricing_multiplier', 1.0);

Object flags

Use getObjectValue(key, defaultValue) for structured configuration data:

const config = client.getObjectValue('promo_banner_config', {
  color: '#00A3FF',
  message: 'Welcome!',
});

Flag evaluation details

When you need more than just the flag value, use the detail methods. These return both the evaluated value and metadata explaining the evaluation:

const details = client.getBooleanDetails('checkout_new', false);

console.log(details.value);       // Evaluated value (true or false)
console.log(details.variant);     // Variant name, if applicable
console.log(details.reason);      // Why this value was chosen
console.log(details.errorCode);   // Error code, if evaluation failed

Complete example

Here’s a complete example showing how to set up and use Datadog Feature Flags in a JavaScript application:

import { DatadogProvider } from '@datadog/openfeature-browser';
import { OpenFeature } from '@openfeature/web-sdk';

// Initialize the Datadog provider
const provider = new DatadogProvider({
  applicationId: '<APPLICATION_ID>',
  clientToken: '<CLIENT_TOKEN>',
  env: '<ENV_NAME>',
});

// Set the evaluation context
const evaluationContext = {
  targetingKey: 'user-123',
  user_id: '123',
  user_role: 'admin',
};

await OpenFeature.setProviderAndWait(provider, evaluationContext);

// Get the client and evaluate flags
const client = OpenFeature.getClient();
const showNewFeature = client.getBooleanValue('new_feature', false);

if (showNewFeature) {
  console.log('New feature is enabled!');
}

Update the evaluation context

To update the evaluation context after initialization (for example, when a user logs in), use OpenFeature.setContext():

await OpenFeature.setContext({
  targetingKey: user.id,
  user_id: user.id,
  email: user.email,
  plan: user.plan,
});