[jennifer-shehane]

• Closes Clarify NYC configration location #947
• Closes Cypress Code Coverage cypress.config.ts file - setupNodeEvents(on, config) error required is not defined #715
• Closes Cannot find coverage file .nyc_output/out.json in the automated build. #528
• Closes component testing suport #596
• Closes Add support for SWC #583

Additional details

This PR fills five documentation gaps that kept coming up in issues, and fixes one bug found while checking them. Each issue lives in its own commit, so it's easy to review them one at a time.

• Where NYC options are read from (Clarify NYC configration location #947). A new Where NYC options are read from section explains that the plugin reads NYC options and the coverage:report script from the folder that holds the Cypress config file. Passing --config-file cypress/cypress.config.ts moves that folder into cypress/, which is what tripped up the reporter. The section lists the supported files and the order they're merged in, and includes a monorepo example.

• ES module import for the task (Cypress Code Coverage cypress.config.ts file - setupNodeEvents(on, config) error required is not defined #715). The Install section now shows import codeCoverageTask from '@cypress/code-coverage/task' next to the require form. On Cypress 15.10 and later, which the plugin requires, both forms work in either kind of config file. The original require is not defined error no longer reproduces. The section also explains that TypeScript's node10 module resolution can't find the plugin's types (TS2307), and which tsconfig.json settings fix it.

• Coverage works locally but not in CI (Cannot find coverage file .nyc_output/out.json in the automated build. #528). A new Coverage works locally but not in CI entry under Common issues covers the usual cause: CI tests an uninstrumented production build. It covers the Babel env and vite-plugin-istanbul defaults, and adds a small spec that fails when window.__coverage__ is missing. This commit also removes the Cannot find coverage file branch from coverageReport in lib/task.ts. saveCoverage writes out.json on the line right before that check, so the branch could never run (and hasn't since v3.13.4).

• Component testing (component testing suport #596). A new Component testing section walks through the support import in cypress/support/component.js, registering the task in component.setupNodeEvents, and instrumenting the dev server with vite-plugin-istanbul or with babel-plugin-istanbul in a webpack config. A new test-apps/component-vite app runs cypress run --component against a React component and checks for 100% coverage.

• SWC and Next.js (Add support for SWC #583). A new Instrument with SWC section shows how to add swc-plugin-coverage-instrument through .swcrc or Next.js experimental.swcPlugins, and explains the SWC plugin version matching that broke things for people in the thread.

  Testing this against a real Next.js 16 app turned up a bug: the report was empty even though window.__coverage__ existed. Next.js runs client component code during hydration, after window:load, and the plugin only captured the coverage object at window:load and at the start of each test. lib/support.ts now reads the window once more in afterEach, before sending coverage. It also reads each page right before it unloads, so a test that visits several such pages keeps all of them. A coverage object that was already captured is updated in place, not sent twice. The new test-apps/swc-webpack app builds with swc-loader and loads its bundle after load. Its test visits two such pages, and reports 0% without the fix and 100% with it.

Both new test apps are in the CI matrix.

Steps to test

1. Read the five README sections linked above.

2. Run npm run build, npm test, and npm run format:check. They should all pass.

3. Run the new test apps:

   npm run build
   cd test-apps/swc-webpack
   npm i
   npm test
   npm run coverage:verify
   npm run coverage:check-files

   Then do the same in test-apps/component-vite.

4. Optionally, run every test app with npm run apps:test:coverage:verify to confirm the lib/support.ts changes don't affect existing setups.

How has the user experience changed?

Apps that create window.__coverage__ after the page's load event, such as Next.js apps instrumented with SWC, now get a coverage report instead of an empty one. Other setups see no change: every existing test app passes with the same coverage as before.

Users also get new README guidance on where NYC options are read from, importing the task from an ES module config file, debugging empty coverage in CI, setting up coverage for component tests, and instrumenting with SWC.

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Generated by Claude Code

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Note

Medium Risk
Changes when browser coverage is sampled in every E2E/component run; behavior is regression-tested via new apps and the full CI matrix, but timing-sensitive apps could see different merge results.

Overview
Fixes late window.__coverage__ collection so apps that populate coverage after window:load (e.g. Next.js hydration / post-load bundles) get full reports. lib/support.ts re-reads coverage on window:before:unload, again in afterEach via cy.window(), and defers sending through cy.then() so counters are flushed before tasks run.

lib/task.ts drops the unreachable “cannot find coverage file” early exit after saveCoverage always writes out.json.

README adds setup/troubleshooting for ES module task imports, component testing (Vite/webpack + NYC excludes), SWC / Next.js instrumentation, where NYC config is resolved (Cypress config folder), and empty coverage in CI; existing NYC/custom-report sections link to that.

CI runs new test-apps/component-vite and test-apps/swc-webpack examples; .gitignore adds .swc/.

^{Reviewed by Cursor Bugbot for commit a11e1b2. Bugbot is set up for automated code reviews on this repo. Configure here.}

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🎉 This PR is included in version 4.1.2 🎉

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