Infinite Scroll with Intersection Observer
Observe a sentinel element at the list bottom and load more when it enters the viewport so there are no page buttons and scrolling is seamless.
Task
Add const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); so the interface remains usable and accessible under the edge cases that manual testing skips.
When to use this
A screen reader user reports the page is unusable because const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); was never implemented, flagged in a support ticket.
Prerequisites
- A frontend component or page in the codebase
- A build with the relevant framework configured
Steps
1. Configure const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); in the project configuration file with the recommended defaults.
const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel);
Expected output: The configuration is accepted and const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); runs without errors on the first invocation.
2. Run the check locally to verify const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); 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 const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); blocks merge on failure.
- name: Run add infinite scroll intersection
run: pnpm test
Expected output: Pull requests with failing const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); 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.
Handle the edge case
Start by measuring the problem. Observe a sentinel element at the list bottom and load more when it enters the viewport so there are no page buttons and scrolling is seamless. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); against the current codebase and inspect the output before wiring it into CI.
const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel);Test with real tools
Once the gate is in place, make failures actionable. A failing const obs = new IntersectionObserver(([e]) => { if (e.isIntersecting) loadMore(); }); obs.observe(sentinel); should point to the exact file and line, not a generic error. Pin the tool version in the lockfile so a upstream release does not silently change behavior. Review the gate output in every pull request just like a test result.