Feature Flags Nodejs

Node.js feature flags installation - Docs

1. 1

   Install the package

   Required

   Install the PostHog Node.js library using your package manager:

   PostHog AI

   npm

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   npm install posthog-node

   yarn

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   yarn add posthog-node

   pnpm

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   pnpm add posthog-node

2. 2

   Initialize PostHog

   Required

   Initialize the PostHog client with your project token:

   Node.js

   PostHog AI

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   import { PostHog } from 'posthog-node'
   const client = new PostHog(
       '<ph_project_token>',
       {
           host: 'https://us.i.posthog.com'
       }
   )

3. 3

   Send an event

   Recommended

   Once installed, you can manually send events to test your integration:

   Node.js

   PostHog AI

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   client.capture({
       distinctId: 'distinct_id_of_the_user',
       event: 'event_name',
       properties: {
           property1: 'value',
           property2: 'value',
       },
   })

4. 4

   Evaluate boolean feature flags

   Required

   Check if a feature flag is enabled:

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   const isFeatureFlagEnabled = await client.isFeatureEnabled('flag-key', 'distinct_id_of_your_user')
   if (isFeatureFlagEnabled) {
       // Your code if the flag is enabled
       // Optional: fetch the payload
       const matchedFlagPayload = await client.getFeatureFlagPayload('flag-key', 'distinct_id_of_your_user', isFeatureFlagEnabled)
   }

5. 5

   Evaluate multivariate feature flags

   Optional

   For multivariate flags, check which variant the user has been assigned:

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   const enabledVariant = await client.getFeatureFlag('flag-key', 'distinct_id_of_your_user')
   if (enabledVariant === 'variant-key') {  // replace 'variant-key' with the key of your variant
       // Do something differently for this user
       // Optional: fetch the payload
       const matchedFlagPayload = await client.getFeatureFlagPayload('flag-key', 'distinct_id_of_your_user', enabledVariant)
   }

6. 6

   Include feature flag information in events

   Required

   If you want to use your feature flag to breakdown or filter events in your insights, you'll need to include feature flag information in those events. This ensures that the feature flag value is attributed correctly to the event.

   Note: This step is only required for events captured using our server-side SDKs or API.

   Set sendFeatureFlags (recommended)

   Set sendFeatureFlags to true in your capture call:

   Node.js

   PostHog AI

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   client.capture({
       distinctId: 'distinct_id_of_your_user',
       event: 'event_name',
       sendFeatureFlags: true,
   })

   Include $feature property

   Include the $feature/feature_flag_name property in your event properties:

   Node.js

   PostHog AI

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   client.capture({
       distinctId: 'distinct_id_of_your_user',
       event: 'event_name',
       properties: {
           '$feature/feature-flag-key': 'variant-key' // replace feature-flag-key with your flag key. Replace 'variant-key' with the key of your variant
       },
   })

7. 7

   Override server properties

   Optional

   Sometimes, you may want to evaluate feature flags using properties that haven't been ingested yet, or were set incorrectly earlier. You can provide properties to evaluate the flag with:

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   await client.getFeatureFlag(
       'flag-key',
       'distinct_id_of_the_user',
       {
           personProperties: {
               'property_name': 'value'
           },
           groups: {
               "your_group_type": "your_group_id",
               "another_group_type": "your_group_id",
           },
           groupProperties: {
               'your_group_type': {
                   'group_property_name': 'value'
               },
               'another_group_type': {
                   'group_property_name': 'value'
               },
           },
       }
   )

8. 8

   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.

9. 9

   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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