fix: include event emitter types from cypress types

[bahmutov]

• closes Cypress types need refactoring #14991 by adding including the event emitter definition where it is used first

User facing changelog

Types no longer complain when you chain event listeners like

Cypress
  .on('test:before:run', () => {
    console.log('before running a test')
  })
  .on('test:after:run', () => {
    console.log('after running a test')
  })

Additional details

Notice the types returned void while the test happily runs. Also moved the emitter reference line into the file where it was used.

How has the user experience changed?

No more type errors

PR Tasks

• Have tests been added/updated?
• Has the original issue or this PR been tagged with a release in ZenHub?

[cypress-bot]

Thanks for taking the time to open a PR!

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.
• Become familiar with the Code Review Checklist for guidelines on coding standards and what needs to be done before a PR can be merged.

[cypress]

---

Test summary

9314 • 0 • 118 • 3 • 1

---

Run details

Project	cypress
Status	Passed
Commit	aef3b47
Started	Feb 9, 2021 3:23 PM
Ended	Feb 9, 2021 3:34 PM
Duration	10:47 💡
OS	Linux Debian - 10.5
Browser	Multiple

View run in Cypress Dashboard ➡️

---

Flakiness

	cypress/integration/retries.ui.spec.js		1
1	runner/cypress retries.ui.spec > opens attempt on each attempt failure for the screenshot, and closes after test passes

---

This comment has been generated by cypress-bot as a result of this project's GitHub integration settings. You can manage this integration in this project's settings in the Cypress Dashboard

[bahmutov]

since we are using NodeEventEmitter type here

[sainthkh]

I became curious that on really returns Cypress. So, I tested with the code below:

it('t', () => {
  console.log(Cypress
  .on('test:before:run', () => {
    console.log('before running a test')
  }).version)
})

And it returned 6.4.0 correctly.

---

In #14991, const cy: Cypress.cy & EventEmitter was mentioned but not covered in this PR.

I tried extending EventEmitter on Cypress.cy definition like interface cy extends Chainable<undefined>, EventEmitter {} but failed because of the clash in property types. It's an open issue since 2017.

Maybe, the easiest solution for this would be adding type cy = Cypress.cy & EventEmitter above cy definition and set the type with it.

[github-actions]

Internal Jira issue: TR-668

[bahmutov]

Yup @sainthkh it returns Cypress - I think that's fine for now, we solve some problems first and leave any other refactoring for another day. Of course judging from purely types we would get

cy.on('...', () => {})
  .version // since now we have returned type `Cypress` and not `cy`, but 🤷‍♂️

I tried interface cy extends Chainable<undefined>, EventEmitter too with same no luck, so again will punt on it

[bahmutov]

Also, I do find it funny that you can combine clashing types when declaring a variable like const cy: Cypress.cy & EventEmitter, but not when extending an interface.

[bahmutov]

I will split #14991 to have the type merge in a separate issue