A common error in Next.js is the hydration error, which I often call the “national error” of Next.js 😅.
📌 What is Hydration?
📌 Why does this error occur?
📌 How can it be resolved?
💡 What is Hydration?
Hydration is the process of making a server-rendered HTML page interactive on the client side using JavaScript.
When a user visits a website 🌐, the page is first rendered on the server before being sent to the browser. Think of it like ordering food online 🍔the restaurant (server) prepares the dish before delivering it to you.
✅ Server rendering improves performance (the browser doesn’t have to render everything from scratch).
✅ It also boosts SEO, allowing Google to crawl the content easily.
Once the HTML arrives at the browser, JavaScript kicks in ⚡, making the page interactive — this process is known as hydration.
❌ Why does a Hydration Error occur?
Hydration errors happen when the server-rendered HTML 🖥️ does not match the client-rendered HTML.
🔥 Example:
Let’s say you display the current time ⏰ inside a
tag using React’s useEffect hook:
`const TimeDisplay = () => {
const [time, setTime] = useState("");
useEffect(() => {
setTime(new Date().toLocaleTimeString());
}, []);
return
{time}
If this component is server-rendered, the initial HTML will not include the time (because useEffect runs only on the client). When the client updates the component, the
tag will now include the current time, causing a mismatch between server and client HTML—resulting in a hydration error.
💡 Important: useEffect runs only on the client, so it shouldn’t be relied upon for pre-rendered server components.
✅ How to Fix Hydration Errors?
🔹 Use static content for server-side rendering whenever possible.
🔹 Handle dynamic data on the client side.
🔹 Wrap dynamic elements inside a useEffect to prevent server-side rendering mismatches.
🚀 By following these best practices, you can avoid hydration errors and build smoother Next.js applications!
