Posthog Sveltekit

Overview

This article provides insight into integrating PostHog with SvelteKit to improve website speed and minimize Cumulative Layout Shift (CLS) when working with feature flags. The author shares their experience with A/B testing and flags for smaller marketing websites and explains their choice of using PostHog due to its freemium tier and clear dashboard analytics. The article also provides a working example of implementing flags and A/B testing.

Features

• Integration of PostHog with SvelteKit: Learn how to integrate PostHog with the SvelteKit framework.
• Minimizing Cumulative Layout Shift (CLS): Understand the importance of minimizing CLS and how it can be achieved when working with feature flags.
• Implementation using PostHog API: Explore the method of using the PostHog API’s /decide route during the initial page load for improved speed and reduced server load.
• Storing and utilizing feature flags: Learn how to set feature flags as a store in the Svelte root layout file and utilize them to show or hide features as needed.
• Avoiding flickering: Discover the approach of updating the featureFlags store and sending an event to PostHog during the onMount function to avoid flickering on the webpage.
• Versatility and customization: Understand how the approach can be tailored to specific needs and expanded to include other functions of the PostHog JavaScript SDK, such as utilizing cookies for user information tracking.

Installation

To integrate PostHog with SvelteKit and implement the described approach, follow these steps:

1. Choose your preferred method of implementing PostHog, such as using the NodeJS SDK, JavaScript SDK, or API.
2. In this case, the author chose to use the PostHog API’s /decide route in conjunction with a Svelte API route during the initial page load.
3. Set the feature flags and local IDs in the server and pass them down to the Svelte root layout file.
4. Initialize the PostHog JavaScript SDK in the Svelte root layout file.
5. Use the onMount function in the layout file to capture page view and page leave data and utilize the featureFlags store to show or hide features as required.
6. Update the featureFlags store during onMount to avoid flickering and send a $feature_flag_called event to PostHog.
7. Customize the implementation based on your specific needs, such as running an API request on page load for critical functions or utilizing cookies for user information tracking.

Summary

This article discusses the integration of PostHog with SvelteKit for implementing feature flags and A/B testing. It emphasizes the importance of minimizing Cumulative Layout Shift and flickering on webpages while maintaining speed and reducing server load. The article provides steps for integrating PostHog using the API approach and explains how to store and utilize feature flags using Svelte’s store feature. It also highlights the versatility and customization options available, such as expanding the usage of the PostHog JavaScript SDK for additional functionality.