React feature flags installation

Install the package

Required

Install posthog-js and @posthog/react using your package manager:

npm install posthog-js @posthog/react
yarn add posthog-js @posthog/react
pnpm add posthog-js @posthog/react

Add environment variables

Required

Add your PostHog API key and host to your environment variables. For Vite-based React apps, use the VITE_PUBLIC_ prefix:

.env
VITE_PUBLIC_POSTHOG_KEY=<ph_project_token>
VITE_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com

Initialize PostHog

Required

Wrap your app with the PostHogProvider component at the root of your application (such as main.tsx if you're using Vite):

main.tsx
import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import './index.css'
import App from './App.jsx'
import { PostHogProvider } from '@posthog/react'

const options = {
  api_host: import.meta.env.VITE_PUBLIC_POSTHOG_HOST,
  defaults: '2026-01-30',
} as const

createRoot(document.getElementById('root')).render(
  <StrictMode>
    <PostHogProvider apiKey={import.meta.env.VITE_PUBLIC_POSTHOG_KEY} options={options}>
      <App />
    </PostHogProvider>
  </StrictMode>
)

defaults option

The defaults option automatically configures PostHog with recommended settings for new projects. See SDK defaults for details.

Accessing PostHog in your code

Recommended

Use the usePostHog hook to access the PostHog instance in any component wrapped by PostHogProvider:

MyComponent.tsx
import { usePostHog } from '@posthog/react'

function MyComponent() {
    const posthog = usePostHog()

    function handleClick() {
        posthog.capture('button_clicked', { button_name: 'signup' })
    }

    return <button onClick={handleClick}>Sign up</button>
}

You can also import posthog directly for non-React code or utility functions:

utils/analytics.ts
import posthog from 'posthog-js'

export function trackPurchase(amount: number) {
    posthog.capture('purchase_completed', { amount })
}

5
Send events
Recommended
Click around and view a couple pages to generate some events. PostHog automatically captures pageviews, clicks, and other interactions for you.
If you'd like, you can also manually capture custom events:
JavaScript
posthog.capture('my_custom_event', { property: 'value' })

Use feature flags

Required

PostHog provides several hooks to make it easy to use feature flags in your React app. Use useFeatureFlagEnabled for boolean flags:

import { useFeatureFlagEnabled } from '@posthog/react'

function App() {
    const showWelcomeMessage = useFeatureFlagEnabled('flag-key')
    const payload = useFeatureFlagPayload('flag-key')
    return (
        <div className="App">
            {showWelcomeMessage ? (
                <div>
                    <h1>Welcome!</h1>
                    <p>Thanks for trying out our feature flags.</p>
                </div>
            ) : (
                <div>
                    <h2>No welcome message</h2>
                    <p>Because the feature flag evaluated to false.</p>
                </div>
            )}
        </div>
    )
}

Multivariate flags

For multivariate flags, use useFeatureFlagVariantKey:

import { useFeatureFlagVariantKey } from '@posthog/react'

function App() {
    const variantKey = useFeatureFlagVariantKey('show-welcome-message')
    let welcomeMessage = ''
    if (variantKey === 'variant-a') {
        welcomeMessage = 'Welcome to the Alpha!'
    } else if (variantKey === 'variant-b') {
        welcomeMessage = 'Welcome to the Beta!'
    }
    return (
        <div className="App">
            {welcomeMessage ? (
                <div>
                    <h1>{welcomeMessage}</h1>
                    <p>Thanks for trying out our feature flags.</p>
                </div>
            ) : (
                <div>
                    <h2>No welcome message</h2>
                    <p>Because the feature flag evaluated to false.</p>
                </div>
            )}
        </div>
    )
}

Flag payloads

The useFeatureFlagPayload hook does not send a $feature_flag_called event, which is required for experiments. Always use it with useFeatureFlagEnabled or useFeatureFlagVariantKey:

import { useFeatureFlagPayload, useFeatureFlagEnabled } from '@posthog/react'

function App() {
    const variant = useFeatureFlagEnabled('show-welcome-message')
    const payload = useFeatureFlagPayload('show-welcome-message')
    return (
        <>
            {variant ? (
                <div className="welcome-message">
                    <h2>{payload?.welcomeTitle}</h2>
                    <p>{payload?.welcomeMessage}</p>
                </div>
            ) : (
                <div>
                    <h2>No custom welcome message</h2>
                    <p>Because the feature flag evaluated to false.</p>
                </div>
            )}
        </>
    )
}

The PostHogFeature component simplifies code by handling feature flag related logic:

App.tsx
import { PostHogFeature } from '@posthog/react'

function App() {
    return (
        <PostHogFeature flag='show-welcome-message' match={true}>
            <div>
                <h1>Hello</h1>
                <p>Thanks for trying out our feature flags.</p>
            </div>
        </PostHogFeature>
    )
}

The match prop can be either true, or the variant key, to match on a specific variant. If you also want to show a default message, you can pass these in the fallback prop.

If your flag has a payload, you can pass a function to children whose first argument is the payload:

App.tsx
<PostHogFeature flag='show-welcome-message' match={true}>
    {(payload) => {
        return (
            <div>
                <h1>{payload.welcomeMessage}</h1>
                <p>Thanks for trying out our feature flags.</p>
            </div>
        )
    }}
</PostHogFeature>

7
Running experiments
Optional
Experiments run on top of our feature flags. Once you've implemented the flag in your code, you run an experiment by creating a new experiment in the PostHog dashboard.

Next steps

Recommended

Now that you're evaluating flags, continue with the resources below to learn what else Feature Flags enables within the PostHog platform.

Resource	Description
Creating a feature flag	How to create a feature flag in PostHog
Adding feature flag code	How to check flags in your code for all platforms
Framework-specific guides	Setup guides for React Native, Next.js, Flutter, and other frameworks
How to do a phased rollout	Gradually roll out features to minimize risk
More tutorials	Other real-world examples and use cases

React feature flags installation

Install the package

Add environment variables

Initialize PostHog

Accessing PostHog in your code

Send events

Use feature flags

Multivariate flags

Flag payloads

Running experiments

Next steps

Community questions

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