🚀 What is Hydration in React?
Hydration is one of those terms that sounds complex at first, but the idea behind it is actually simple.
When we use Server Side Rendering (SSR), the server sends ready-made HTML to the browser. Because the HTML is already generated, the page appears on the screen very quickly.
But at this moment, the page is only static — buttons don’t work, and there is no interaction yet.
Then React loads the JavaScript bundle in the browser.
After the JavaScript loads, React attaches event listeners and logic to the existing HTML.
This process of connecting React with the already rendered HTML is called Hydration.
👉 In simple words:
Hydration = React making server-rendered HTML interactive.
⚠️ Why does a Hydration Error happen?
A hydration error happens when the HTML generated on the server is different from what React renders on the client.
React tries to match both versions of the UI. If they don’t match, React throws a hydration error.
Common reasons include:
• Using Math.random() during rendering
• Using Date.now()
• Rendering content that depends on window or browser APIs
• Conditional rendering that behaves differently on server and client
💡 Key Takeaway
When working with SSR frameworks like Next.js, the initial UI generated on the server and the client must be the same. Otherwise, React cannot hydrate the page correctly.
💬 Have you ever faced a hydration error while working with React or Next.js?
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