The Hidden Pitfalls of Server-Side Rendering in Gatsby
A Common Conundrum
If you’ve been developing Gatsby applications lately, you’ve likely encountered a frustrating issue. Your app stores user data in the client’s browser, perhaps in Local Storage. You want to make UI changes based on individual data, such as theme preferences or login details. Everything works smoothly locally, but when you deploy, things don’t quite go as planned. What’s going on?
The Rehydration Issue
This problem is known as a rehydration issue. React and Gatsby struggle to match data from the server with changes made on the client. This occurs because React doesn’t expect mismatches between what was statically generated on the server and what was rendered by the client.
How Gatsby Works
To understand the root of the problem, let’s dive into Gatsby’s server-side rendering (SSR) features. Gatsby can render complex pages on the server and send the full output to the client. This differs from regular React applications, which are generated entirely on the client. With SSR, you send the rendered content, resulting in faster page loads and improved performance metrics.
The Caveat
However, there’s a catch. If your page is server-side rendered, but you need client-only information to complete the UI, you have a problem. Suppose you need to display a login button for visitors and a logout button for users. If the login information is stored only on the client, how can the server-side rendered page know which button to display before the JavaScript loads?
The Annoying Consequences
This can lead to frustrating events, such as the page displaying the wrong button initially and then switching to the correct one after JavaScript evaluation. It gets worse if the buttons are conditionally rendered based on client-side data and have different styles. You might end up with mixed-up styles and unexpected colors!
The Solution
Fortunately, there’s a simple way to overcome this problem. We can mitigate the issue by deferring the rendering of specific elements until the client has fully loaded. By holding off rendering until the client has acted, we can ensure the integrity of the UI.
Using React Hooks to the Rescue
We can leverage React Hooks to detect whether the code is running on the server or client. By using the useEffect hook with an empty dependency array, we can determine if the code is running on the client or server. This allows us to conditionally render elements based on client-side data.
Visualizing the Issue
The rehydration problem and its workarounds can be easily observed in a simple example. The first button demonstrates the rehydration issue, while the second button fixes the issue but still displays a flicker. The third button only renders after the JavaScript is fully evaluated, avoiding the flicker altogether.
Key Takeaways
To avoid the rehydration issue in Gatsby applications:
- Use the
keyattribute when your component changes depending on the rendering context. - Prevent the component from rendering until you acknowledge that the application is running on the client to avoid flicker.
- Adopt a custom Hook, such as
useIsClient, to reuse the necessary logic for accomplishing the above points.
By following these guidelines, you can ensure a seamless user experience and avoid the pitfalls of server-side rendering in Gatsby.