Understanding partial hydration in Gatsby 5

Gatsby's latest version, v5, introduces the beta feature of partial hydration, allowing developers to selectively add interactivity to static apps, thereby enhancing frontend performance while preserving client-side application benefits. This new feature addresses the challenge in React-based apps where all JavaScript must be downloaded before interactivity, impacting the Time to Interactive (TTI) metric. Partial hydration enables the hydration of only necessary JavaScript for React components, reducing bundle sizes and speeding up page loads. Implemented using React server components, partial hydration allows developers to render static and interactive components selectively, such as on pages with mostly static content but a few interactive elements like forms or buttons. Known limitations include incompatibility with styling libraries like Emotion and Styled-components, as well as the gatsby-plugin-offline, which currently does not support partial hydration. Although partial hydration is still in beta, it promises significant improvements in user experience and performance by decreasing JavaScript payloads, with the caveat of possible future breaking changes as the feature evolves.