Split Bundles at Route Level for Faster Loads
Configure dynamic imports per route so the initial bundle is 40KB not 400KB and each page loads only its own code.
Task
Apply const Page = lazy(() => import('./pages/Settings')); 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 const Page = lazy(() => import('./pages/Settings'));, scoring 72 on mobile.
Prerequisites
- A Lighthouse or WebPageTest baseline measurement
- Access to the build configuration
Steps
1. Configure const Page = lazy(() => import('./pages/Settings')); in the project configuration file with the recommended defaults.
const Page = lazy(() => import('./pages/Settings'));
Expected output: The configuration is accepted and const Page = lazy(() => import('./pages/Settings')); runs without errors on the first invocation.
2. Run the check locally to verify const Page = lazy(() => import('./pages/Settings')); 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 Page = lazy(() => import('./pages/Settings')); blocks merge on failure.
- name: Run add bundle split route level
run: pnpm test
Expected output: Pull requests with failing const Page = lazy(() => import('./pages/Settings')); 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. Configure dynamic imports per route so the initial bundle is 40KB not 400KB and each page loads only its own code. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run const Page = lazy(() => import(‘./pages/Settings’)); against the current codebase and inspect the output before wiring it into CI.
const Page = lazy(() => import('./pages/Settings'));Verify the improvement
Once the gate is in place, make failures actionable. A failing const Page = lazy(() => import(‘./pages/Settings’)); 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.