chore: Eslint migration foundation + migrate npm/grep package

[cacieprins]

Additional details

This is a pared down PR related to #30892

It includes:

• The new shared eslint config
• A migration guide, including troubleshooting steps discovered while migrating npm/grep
• An example migration in ./npm/grep

Steps to test

How has the user experience changed?

PR Tasks

• [NA] Have tests been added/updated?
• [NA] Has a PR for user-facing changes been opened in cypress-documentation?
• [NA] Have API changes been updated in the type definitions?

[jennifer-shehane]

@MikeMcC399 Might be curious to get your eyes on this (if you have time), since you've been handling eslint config in the other repos so nicely. Particularly the guide outline.

[cypress]

cypress    Run #64171

Run Properties:   Passed #64171  •  3488c406e4: lockfile

Project	cypress
Branch Review	eslint-migration-foundation
Run status	Passed #64171
Run duration	19m 23s
Commit	3488c406e4: lockfile
Committer	Cacie Prins
View all properties for this run ↗︎

---

Test results
Failures	0
Flaky	11
Pending	1232
Skipped	0
Passing	32177
View all changes introduced in this branch ↗︎

UI Coverage  45.96%
Untested elements	189
Tested elements	165

Accessibility  97.95%
Failed rules	3 critical   8 serious   2 moderate   2 minor
Failed elements	107

[MikeMcC399]

Consider upgrading to eslint-plugin-mocha@11

[MikeMcC399]

@jennifer-shehane

Might be curious to get your eyes on this (if you have time), since you've been handling eslint config in the other repos so nicely. Particularly the guide outline.

I only have some general comments:

• It's good to see a staged approach!

• If updates to @cypress/eslint-plugin-dev are no longer to be published to the npm registry, then the other repos using this module would need an alternate strategy for linting:

  • https://github.com/cypress-io/cypress-example-recipes
  • https://github.com/cypress-io/cypress-watch-preprocessor
  • https://github.com/cypress-io/get-windows-proxy

• I would recommend using the latest eslint@9 version, currently v9.31.0 (see https://eslint.org/). ESLint is continually making improvements that also affect ease-of-use and configuration.

• Some of the other dependencies are outdated (like eslint-plugin-cypress@4). Use latest versions unless there are compatibility issues preventing this.

[cacieprins]

@MikeMcC399 Thank you so much for the feedback!

[cacieprins]

@MikeMcC399 I'm considering whether, after the migration in this repo, switching eslint-config out to the npm package as a major version upgrade. It's not right now to allow for a progressive migration in this repo, though. Thanks for bringing that up!

[AtofStryker]

Do you remember why we needed to touch the tsconfig here?

[cacieprins]

To get eslint to pick up on everything. The new eslint config runs .js files through typescript linter - this helps it lint interactions between js and ts. If typescript eslint matches a file that isn't in the "default project" (e.g., not matched by the closest tsconfig), it throws an error.

[AtofStryker]

is jiti a peer dependency or something that we need to include here?

[cacieprins]

jiti is a dependency of an updated eslint plugin, but a few dependencies of frontend-shared depend on an older version of jiti. Yarn doesn't install the version that one of the eslint pugins here needs, so node uses thet older version of jiti via hoisting. Declaring it here prevents it from using the hoisted version.

[AtofStryker]

in other words we need to disable these rules temporarily because there is an overwhelming amount of errors?

[cacieprins]

yep, they're not currently rules that are applied to the project, but ones that would be good to turn on - they are defaulted on in the recommended rules.