Virtual Scroll Large Lists for Constant DOM
Render only the visible window of a 10000-row list so the DOM stays under 100 nodes and scrolling is smooth.
Task
Apply <VirtualList items={rows} itemSize={40} renderItem={Row} /> to reduce a measured bottleneck that shows up in the performance budget or Lighthouse audit.
When to use this
Lighthouse reports the page fails the performance budget because of <VirtualList items={rows} itemSize={40} renderItem={Row} />, scoring 72 on mobile.
Prerequisites
- A Lighthouse or WebPageTest baseline measurement
- Access to the build configuration
Steps
1. Configure <VirtualList items={rows} itemSize={40} renderItem={Row} /> in the project configuration file with the recommended defaults.
<VirtualList items={rows} itemSize={40} renderItem={Row} />
Expected output: The configuration is accepted and <VirtualList items={rows} itemSize={40} renderItem={Row} /> runs without errors on the first invocation.
2. Run the check locally to verify <VirtualList items={rows} itemSize={40} renderItem={Row} /> produces the expected result before pushing.
pnpm test
Expected output: Local run matches CI behavior; no surprises after push.
3. Add the gate to the CI pipeline so <VirtualList items={rows} itemSize={40} renderItem={Row} /> blocks merge on failure.
- name: Run add virtual scroll large list
run: pnpm test
Expected output: Pull requests with failing <VirtualList items={rows} itemSize={40} renderItem={Row} /> are blocked from merging.
Troubleshooting
Problem
The check passes locally but fails in CI
Solution
Pin dependency versions and the runtime to match CI exactly; reproduce with the same Docker image or act.
Problem
Configuration is rejected with a schema error
Solution
Check the tool version matches the config schema; older versions may not support newer fields.
Limitations
- The gate only runs on events that trigger the workflow; locally pushed commits bypass it.
- Configuration drift is possible if someone edits settings outside version control.
Measure before optimizing
Start by measuring the problem. Render only the visible window of a 10000-row list so the DOM stays under 100 nodes and scrolling is smooth. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run
<VirtualList items={rows} itemSize={40} renderItem={Row} />Verify the improvement
Once the gate is in place, make failures actionable. A failing