sveltejs / svelte · Issue No. 18780

Discussion: Improving hydration performance for large lists

Openby fbwe425opened Sep 6, 2026updated Sep 22, 20260 comments

perf

Description

When working with large lists (1000+ items) in SvelteKit, hydration can be noticeably slow compared to the initial SSR render. This affects Time to Interactive (TTI) metrics significantly.

Reproduction

Rendering a list of 2000 items with dynamic content shows a 300-500ms hydration delay on mid-range devices.

Suggestion

Consider implementing virtual hydration or lazy hydration strategies:

Only hydrate visible items initially
Defer hydration of off-screen items until they enter the viewport
Provide a lazy directive for components that can be hydrated later

This would significantly improve TTI for content-heavy pages like e-commerce listings or social feeds.

Relay Analysis

View on GitHub

Relay reads this issue against the repository's contribution signals: the files it is likely to touch, how the maintainers triage work this size, and what the first contribution would exercise.

The full analysis for this issue is still being assembled. Until then, the description above and the thread on GitHub are the most reliable context.