virtualized-lists
Render only visible rows for long lists (1k+ rows) using intersection observer or lightning-datatable virtual scroll. NOT for simple lists under 100 rows.
Best use case
virtualized-lists is best used when you need a repeatable AI agent workflow instead of a one-off prompt.
Render only visible rows for long lists (1k+ rows) using intersection observer or lightning-datatable virtual scroll. NOT for simple lists under 100 rows.
Teams using virtualized-lists should expect a more consistent output, faster repeated execution, less prompt rewriting.
When to use this skill
- You want a reusable workflow that can be run more than once with consistent structure.
When not to use this skill
- You only need a quick one-off answer and do not need a reusable workflow.
- You cannot install or maintain the underlying files, dependencies, or repository context.
Installation
Claude Code / Cursor / Codex
Manual Installation
- Download SKILL.md from GitHub
- Place it in
.claude/skills/virtualized-lists/SKILL.mdinside your project - Restart your AI agent — it will auto-discover the skill
How virtualized-lists Compares
| Feature / Agent | virtualized-lists | Standard Approach |
|---|---|---|
| Platform Support | Not specified | Limited / Varies |
| Context Awareness | High | Baseline |
| Installation Complexity | Unknown | N/A |
Frequently Asked Questions
What does this skill do?
Render only visible rows for long lists (1k+ rows) using intersection observer or lightning-datatable virtual scroll. NOT for simple lists under 100 rows.
Where can I find the source code?
You can find the source code on GitHub using the link provided at the top of the page.
SKILL.md Source
# LWC Virtualized Lists Rendering 10,000 DOM nodes crashes mobile and lags desktop. Virtualization renders only ~2 screens worth of rows and swaps them as the viewport scrolls. `lightning-datatable` has built-in infinite scroll; for custom layouts use an IntersectionObserver-based pattern with fixed row height. This skill covers both paths plus the accessibility requirements (aria-rowcount, keyboard reachability) that are easy to miss when optimizing for performance. ## Adoption Signals Lists beyond 500 rows or tables beyond 1000. Not for simple short lists. - Required when initial render time exceeds 500ms or the user reports janky scroll on lower-end devices. - Required for tables with computed columns (formulas, joins) where each row's render cost compounds. ## Recommended Workflow 1. Measure: if first render <100ms, skip virtualization. 2. `lightning-datatable enable-infinite-loading` + `onloadmore` handler that paginates server-side. 3. Custom: fixed row height + IntersectionObserver sentinels + windowed render of visible + buffer rows. 4. Cache row data client-side; server returns pages of 50–200. 5. Test with 10,000-row fixture to measure FPS and memory. ## Key Considerations - Variable row heights break naive virtualization; use a measured-height library or fix the height. - Screen readers must see a meaningful row count (`aria-rowcount`). - Keyboard navigation must still reach off-screen rows logically. - Server pagination > client-side filtering for 10k+ datasets. ## Worked Examples (see `references/examples.md`) - *10k-row datatable* — Audit log viewer - *Custom list with IO* — Activity feed ## Common Gotchas (see `references/gotchas.md`) - **Variable row height** — Items jump around on scroll. - **aria-rowcount missing** — Screen reader reports 'list with 20 items' on a 10k list. - **Client-side filter on big list** — Re-filters 10k rows on each keystroke; jank. ## Top LLM Anti-Patterns (full list in `references/llm-anti-patterns.md`) - Rendering 10k rows directly - Client-side filter on huge datasets - Missing aria-rowcount ## Official Sources Used - Lightning Web Components Developer Guide — https://developer.salesforce.com/docs/platform/lwc/guide/ - Lightning Data Service — https://developer.salesforce.com/docs/platform/lwc/guide/data-wire-service-about.html - LWC Recipes — https://github.com/trailheadapps/lwc-recipes - SLDS 2 — https://www.lightningdesignsystem.com/2e/
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