Adding experiment code

Once you've created your experiment in PostHog, the next step is to add your code.

Fetch the feature flag

In your experiment, each user is randomly assigned to a variant (usually either 'control' or 'test'). To check which variant a user has been assigned to, fetch the experiment feature flag. You can then customize their experience based on the value in the feature flag:

// Ensure flags are loaded before usage.
// You only need to call this on the code the first time a user visits.
// See this doc for more details: /docs/feature-flags/manual#ensuring-flags-are-loaded-before-usage
posthog.onFeatureFlags(function() {
    // feature flags should be available at this point
    if (posthog.getFeatureFlag('experiment-feature-flag-key')  == 'variant-name') {
        // do something
    }
})

// Otherwise, you can just do:
if (posthog.getFeatureFlag('experiment-feature-flag-key')  == 'variant-name') {
    // do something
}

// You can also test your code by overriding the feature flag:
// e.g., posthog.featureFlags.overrideFeatureFlags({ flags: {'experiment-feature-flag-key': 'test'}})

Since feature flags are not supported yet in our Java and Rust SDKs, to run an experiment using these SDKs see our docs on how to run experiments without feature flags. This also applies to running experiments using our API.

PostHog is an all-in-one developer platform for building successful products. We provide product analytics, web analytics, session replay, error tracking, feature flags, experiments, surveys, LLM analytics, data warehouse, CDP, and an AI product assistant to help debug your code, ship features faster, and keep all your usage and customer data in one stack.

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