@feathq/js-sdk

Server-side JavaScript / TypeScript SDK for feat feature flags. Local flag evaluation against a polled datafile, OpenFeature provider included.

For browser code, use @feathq/web-sdk. For edge runtimes via service binding, use @feathq/worker-sdk.

Install

npm install @feathq/js-sdk
# or
yarn add @feathq/js-sdk

Node.js 18+ (built-in fetch). Bun and Deno are supported.

Usage

import { FeatClient } from "@feathq/js-sdk";

const client = new FeatClient({
  apiKey: process.env.FEAT_SERVER_KEY!,    // feat_sdk_…
  dataPlaneUrl: "https://data.feat.so",
});

await client.ready();

const result = await client.evaluate("checkout-v2", false, {
  targetingKey: "user-123",
  user: { plan: "pro", email: "alice@example.com" },
});

if (result.value) {
  // …
}

Use a server API key (feat_sdk_…). Mobile and client-side keys are for the mobile and browser SDKs respectively.

OpenFeature

import { OpenFeature } from "@openfeature/server-sdk";
import { FeatClient, FeatProvider } from "@feathq/js-sdk";

const featClient = new FeatClient({ apiKey, dataPlaneUrl });
await OpenFeature.setProviderAndWait(new FeatProvider(featClient));

const client = OpenFeature.getClient();
const enabled = await client.getBooleanValue("checkout-v2", false, {
  targetingKey: "user-123",
});

How it works

• The SDK fetches a per-environment datafile and keeps it in memory.
• Polls every 30 s by default (configurable down to 5 s). ETag-aware: unchanged polls are 304s.
• Evaluation is local; no per-flag network call.
• dataPlaneUrl must use https:// (the constructor rejects plaintext URLs except http://localhost for tests).

License

MIT