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Cloudflare SDK reference

Read time: 4 minutes
Last edited: Aug 15, 2023
Version 2 of the Cloudflare SDK replaces users with contexts

A context is a generalized way of referring to the people, services, machines, or other resources that encounter feature flags in your product. Contexts replace another data object in LaunchDarkly: "users."

Code samples on this page are from the two most recent SDK versions where they differ. To learn more about upgrading, read Cloudflare 1.x to 2.0 migration guide and Best practices for upgrading users to contexts.


This topic documents how to get started with the Cloudflare SDK, and links to reference information on all of the supported features.

SDK quick links

LaunchDarkly's SDKs are open source. In addition to this reference guide, we provide source, API reference documentation, and sample applications:

SDK API documentationSDK API docs
GitHub repositoryjs-core/packages/sdk/cloudflare
Sample applicationExample app
Published modulenpm
This SDK requires LaunchDarkly's Cloudflare integration

Configure the Cloudflare integration to use this SDK successfully. To learn more, read Cloudflare.

The Cloudflare integration is available to customers on an Enterprise plan. To learn more, read about our pricing. To upgrade your plan, contact Sales.

For use in Cloudflare Workers only

This SDK is intended only for use in multi-user Cloudflare Workers. Choose one of the other JavaScript-based SDKs for browser, server, or mobile environments.

Client-side browser environments:

  • For React applications, read the React SDK reference.
  • For Vue applications, read the Vue SDK reference.
  • For all other client-side browser JavaScript applications, read the JavaScript SDK reference.

Non-browser environments:

To learn more about LaunchDarkly's different SDK types, read Client-side and server-side SDKs.

Daemon mode

The Cloudflare SDK operates in daemon mode using the Cloudflare KV as a persistent feature store without connecting to LaunchDarkly. The Cloudflare SDK does not support streaming and does not send any analytics events to LaunchDarkly.

To learn more, read Persistent data stores.

Getting started

After you complete the Getting Started process, follow these instructions to start using the LaunchDarkly SDK in your Cloudflare Worker.

First, install the LaunchDarkly SDK as a dependency in your application using your application's dependency manager.

Here's how:

yarn add @launchdarkly/cloudflare-server-sdk

Then turn on the Node.js compatibility flag in your wrangler.toml. This allows the SDK to use node:events:

compatibility_flags = [ "nodejs_compat" ]

Next, import the LaunchDarkly client in your application code:

import { init } from '@launchdarkly/cloudflare-server-sdk';
The Cloudflare SDK uses a client-side ID

The Cloudflare SDK uses a client-side ID to associate the LaunchDarkly environment with the CDN integration. Your environment's client-side ID is available in the Projects tab of your Account settings page. To learn more about key types, read Keys.

After you install and import the SDK, create an instance of LDClient. Specify your client-side ID and Cloudflare KV namespace here. The client-side ID is only used to query the KV namespace, not to connect with LaunchDarkly servers.

Here's how:

const client = init(sdkKey, env.LD_KV);
await client.waitForInitialization();

Await the waitForInitialization function after you initialize the client. When waitForInitialization is resolved the client can serve feature flags.

Using client, you can check which variation a particular context will receive for a given feature flag. In your Cloudflare Worker application, place the client.variation code so that it is invoked as needed.

Here is an example:

const context = {
"kind": 'user',
"key": 'user-key-123abc',
"name": 'Sandy'
const flagValue = await client.variation('flag-key-123abc', context, false);

Example Worker

This is an example Cloudflare Worker application that initializes the ldClient and evaluates a feature flag for a context.

import { init } from '@launchdarkly/cloudflare-server-sdk';
export default {
async fetch(request: Request, env: Bindings): Promise<Response> {
const context = { kind: 'user', key: 'test-user-key-1' };
// init the ldClient, wait and finally evaluate
const client = init('sdk-key', env.LD_KV);
await client.waitForInitialization();
const flagValue = await client.variation('flag-key', context, false);
return new Response(`${flagValue}`);

Read the full example in GitHub.

Promises and async

All asynchronous SDK methods that return a Promise are compatible with then/catch or async/await. You can use either.

Shut down the client

Shut down the client when your application terminates. To learn more, read Shutting down.

Supported features

This SDK supports the following features: