Question 1

What is hydration in Angular?

Accepted Answer

Client Angular attaches listeners and state to server-rendered DOM instead of recreating it. Non-destructive hydration reuses DOM nodes. Mismatches cause errors or re-renders. Keep server/client markup consistent.

Question 2

What causes hydration mismatches?

Accepted Answer

Different content on server vs client: random IDs, time-dependent text, browser-only branches, invalid HTML nesting. Use afterNextRender for client-only bits. Stabilize IDs. Validate HTML structure.

Question 3

What is incremental/partial hydration conceptually?

Accepted Answer

Hydrating parts of the page on demand rather than the entire app at once. Improves TTI for large pages. Combine with @defer. Still evolving—know the current Angular APIs you use.

Question 4

How do you verify hydration is working in production?

Accepted Answer

Check for hydration errors in console, confirm no full DOM wipe, and measure interaction readiness. Monitor RUM metrics. Fix mismatches before relying on SSR SEO wins.

Hydration Angular Interview Questions

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