flowbits

Feature flags for Node.js: on/off toggles, percentage rollouts, A/B variants, user overrides, and targeting rules.

Zero runtime dependencies. Node 18+.

Package name: flowbits (unscoped — install with npm install flowbits)

Install

npm install flowbits

Quick start

import { createClient } from "flowbits";

const flags = createClient({
  flags: {
    darkMode: true,
    checkoutV2: {
      enabled: true,
      percentage: 25,
      variants: { control: 50, new: 50 },
      rules: [
        {
          when: { field: "plan", op: "eq", value: "pro" },
          percentage: 100,
          variant: "new",
        },
      ],
      overrides: {
        "user_ada": true,
      },
    },
  },
});

flags.isEnabled("darkMode"); // true

flags.evaluate("checkoutV2", { id: "user_ada", plan: "free" });
// { key: "checkoutV2", enabled: true, variant: null, reason: "override" }

flags.variant("checkoutV2", { id: "user_42", plan: "pro" });
// "new"

Flag shapes

// Simple on/off
{ betaBanner: true }

// Rollout + variants + rules
{
  searchRewrite: {
    enabled: true,
    percentage: 10,          // % of users who get the flag
    defaultVariant: "control",
    variants: { control: 1, treatment: 1 },
    rules: [
      {
        when: { all: [
          { field: "country", op: "in", value: ["US", "CA"] },
          { field: "age", op: "gte", value: 18 },
        ]},
        percentage: 100,
        variant: "treatment",
      },
    ],
    overrides: {
      "staff_1": { enabled: true, variant: "treatment" },
    },
  },
}

Targeting operators

eq neq gt gte lt lte in nin contains startsWith endsWith exists regex between

Combine with all, any, and not.

API

| Method | Purpose | | --- | --- | | createClient(config) / new Flowbits(config) | Create a client | | isEnabled(key, context) | Boolean check | | variant(key, context, fallback?) | A/B variant name | | evaluate(key, context) | Full result + reason | | all(context) | Evaluate every flag | | define / remove / load / merge | Manage flags at runtime | | bucket / inRollout / assignVariant | Low-level hashing helpers |

Subject id is taken from context.id, context.userId, context.key, or context.subject.

License

MIT