Trap Focus Inside a Modal Dialog
Move focus to the modal on open, cycle within, and restore to the trigger on close so keyboard users cannot tab behind the overlay.
Task
Add const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); 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 trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); 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 trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); in the project configuration file with the recommended defaults.
const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate();
Expected output: The configuration is accepted and const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); runs without errors on the first invocation.
2. Run the check locally to verify const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); 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 trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); blocks merge on failure.
- name: Run add modal focus trap
run: pnpm test
Expected output: Pull requests with failing const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); 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. Move focus to the modal on open, cycle within, and restore to the trigger on close so keyboard users cannot tab behind the overlay. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); against the current codebase and inspect the output before wiring it into CI.
const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate();Test with real tools
Once the gate is in place, make failures actionable. A failing const trap = createFocusTrap(modalEl); trap.activate(); // on close: trap.deactivate(); 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.