feat Node.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_…
  url: "https://data-01.feat.so",          // optional; this is the default
});

await client.ready();

const result = await client.evaluate("checkout-v2", false, {
  targetingKey: "user-123",
  user: { plan: "pro", email: "[email protected]" },
});

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 });
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.
• Live streaming is on by default. After the initial fetch the SDK opens a Server-Sent Events stream and applies each pushed datafile the moment it changes. Updates are applied in version order: a push is adopted only when its version is strictly newer than the one in memory.
• A background poll keeps running as a safety net (slow while the stream is healthy). If the stream cannot establish or drops, the SDK falls back to polling at the normal interval and keeps retrying the stream with backoff.
• Set streaming: false to rely on polling alone. Poll cadence is pollIntervalMs (default 30 s, floored at 5 s). ETag-aware: unchanged polls are 304s.
• Evaluation is local; no per-flag network call.
• Call client.close() to tear down the stream and poll loop.
• url must use https:// if you override it (the constructor rejects plaintext URLs except http://localhost for tests).

License

MIT