Omnibus Instrument Feature Flags

React feature flags installation - Docs

1. 1

   Install the package

   Required

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

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   npm

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   npm install posthog-js @posthog/react

   yarn

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   yarn add posthog-js @posthog/react

   pnpm

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   pnpm add posthog-js @posthog/react

2. 2

   Add environment variables

   Required

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

   .env

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

3. 3

   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

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   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_PROJECT_TOKEN} options={options}>
         <App />
       </PostHogProvider>
     </StrictMode>
   )

   defaults option

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

4. 4

   Accessing PostHog in your code

   Recommended

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

   MyComponent.tsx

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   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

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

5. 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

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   posthog.capture('my_custom_event', { property: 'value' })

6. 6

   Use feature flags

   Required

   Using hooks

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

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   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:

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   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:

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   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>
               )}
           </>
       )
   }

   Using PostHogFeature component

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

   App.tsx

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   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

   PostHog AI

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   <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. 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.

8. 8

   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

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