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frontendhard

What is React Hydration and why does it cause mismatches?

✓ Decoded Answer

Hydration is the process where client-side JavaScript attaches event listeners and initial state to the static HTML delivered by Server-Side Rendering (SSR). A mismatch occurs when the server-rendered HTML differs from the client's initial render (e.g. referencing 'window' variables, using random numbers, or dynamic date objects directly in the markup).

// Causes Hydration Mismatch
const Timer = () => <span>{new Date().toLocaleTimeString()}</span>;

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