Technical Definition
Hydration is the process of attaching JavaScript functionality to server-rendered HTML in the browser. Relevant for SSR frameworks. SEO consideration: content is crawlable before hydration, but hydration time affects interactivity (INP). Partial hydration and progressive hydration are emerging patterns.
Simple Explanation (ELI13)
Hydration is when JavaScript takes over a page that was already rendered by the server. The HTML is already there (good for SEO), then JavaScript makes it interactive. If hydration is slow, your INP (interactivity) score suffers. New techniques make this faster.
Related Terms
SSR, JavaScript, INP, Core Web Vitals
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