@sandsoftwaresolutions/feature-flags

Predictable, edge-friendly feature flags without a database or external service.

Install

npm install @sandsoftwaresolutions/feature-flags

Usage

import { evaluate } from "@sandsoftwaresolutions/feature-flags";

const flag = { key: "new-checkout", rollout: 15, allow: ["qa-user"], deny: ["blocked-user"] };
const enabled = evaluate(flag, { id: user.id });

How it works

evaluate(flag, context) returns a boolean. enabled: false always disables a flag; deny overrides all other rules; an allow list limits access to listed subjects; then rollout applies a deterministic 0–100 percentage. The same key and user ID always have the same result, so users do not jump in and out of an experiment.

Use inRollout(key, subject, percentage) when you only need the stable percentage decision. Flags are configuration, not authorization: enforce permissions separately on the server.