---
type: Glossary Term
title: "Hydration"
description: "The process of attaching JavaScript event listeners to server-rendered HTML in the browser."
resource: "https://prerendering.com/glossary/hydration"
tags: [rendering, glossary]
timestamp: 2026-05-11T00:00:00Z
---

# Hydration

The process of attaching JavaScript event listeners to server-rendered HTML in the browser.

After server-rendered HTML arrives in the browser, the JavaScript framework "hydrates" it — running again on the client to attach event handlers and reactive state. Hydration mismatches (server HTML differs from client render) cause warnings and can change canonical tags or page metadata after first paint, which crawlers may or may not see.

## Related

- [Canonical Issues on JavaScript Websites](/blog/canonical-issues-on-javascript-websites.md)