Partial hydration in Gatsby is a feature that allows you to selectively hydrate client components on the server, while still keeping the benefits of client-side apps. This approach can lead to improved frontend performance and faster page loads.

To use partial hydration in Gatsby, you need to enable the PARTIAL_HYDRATION flag in the gatsby-config file. Then, you can mark specific components as “use client” to indicate that they should be hydrated on the client-side.

Some known issues with partial hydration include:

• Styling libraries like emotion and styled-components do not currently work when partial hydration is enabled.
• React Server Components is not supported.
• gatsby-plugin-offline is not supported and may cause build failures.

Partial hydration is still in beta and has some limitations. However, it can provide significant performance improvements for pages with interactive components.

To learn more about partial hydration with Gatsby 5, check out the RFC and the conceptual guide.

Here’s a quick example of how to use partial hydration in Gatsby:

1. Install the latest version of Gatsby and experimental versions of React and react-dom.
2. Enable the PARTIAL_HYDRATION flag in the gatsby-config file.
3. Mark specific components as “use client” to indicate that they should be hydrated on the client-side.

For example:

“`
// src/components/demo.js
import React from ‘react’;

const Demo = () => {
const [count, setCount] = React.useState(0);

return (

);
};

export default Demo;
“`

“`
// src/pages/using-partial-hydration.js
import React from ‘react’;
import Demo from ‘../components/demo’;

const Page = () => {
return (

);
};

export default Page;
“`

By marking the Demo component as “use client”, we’re telling Gatsby to hydrate it on the client-side, while still keeping the benefits of server-side rendering for the rest of the page.

Keep in mind that partial hydration is still in beta and has some limitations. However, it can provide significant performance improvements for pages with interactive components.