Targeting & Rollouts

How GrowthBook Evaluates a Flag

Every Feature in GrowthBook has a set of Rules per environment (e.g. dev, production). When the SDK calls isOn() or getFeatureValue(), GrowthBook walks through those rules from top to bottom. The first rule whose targeting condition matches the current user’s attributes is applied and its value is returned. If no rule matches, the Feature’s default value is returned.

This top-down, first-match model gives you precise control: you can force a value for internal users, then run a percentage rollout for everyone else, and the two rules will never interfere.

Module lessons

#	Lesson	What you will learn
1	Overview (this page)	How rule evaluation works end-to-end
2	Targeting Attributes	Defining and passing user attributes to the SDK
3	Targeting Conditions	Filtering users by attribute value in a rule
4	Percentage Rollouts	Gradually releasing a flag to a percentage of users
5	Forced Values & Saved Groups	Forcing specific values and reusing user segments

import { GrowthBook } from '@growthbook/growthbook';

const gb = new GrowthBook({
  apiHost: 'https://cdn.growthbook.io',
  clientKey: 'sdk-YOUR_DEV_KEY',
});

await gb.init({ timeout: 2000 });

// Tell GrowthBook who the current user is
gb.setAttributes({
  id: 'user-123',
  country: 'TH',
  plan: 'pro',
});

// Boolean flag
const showBanner = gb.isOn('promo-banner');

// Flag with a typed default
const checkoutVersion = gb.getFeatureValue('checkout-version', 'v1');

import { GrowthBook } from '@growthbook/growthbook';

const gb = new GrowthBook({
  apiHost: 'https://cdn.growthbook.io',
  clientKey: 'sdk-YOUR_DEV_KEY',
});

await gb.init({ timeout: 2000 });

// Tell GrowthBook who the current user is
gb.setAttributes({
  id: 'user-123',
  country: 'TH',
  plan: 'pro',
});

// Boolean flag
const showBanner = gb.isOn('promo-banner');

// Flag with a typed default
const checkoutVersion = gb.getFeatureValue('checkout-version', 'v1');