testing-library
Add ability for users to supply generic type
What: Add ability to supply generic types similar to Cypress's API
Why:
This allows for further narrowing elements returned by queries in tests instead of just HTMLElement for every element
How:
Update types to include generic <E extends Node = HTMLElement>
Ran npx dslint types locally and validated ExpectType tests still passed
Checklist:
- [ ] Documentation
- [X] Tests
- [X] Ready to be merged
Not sure who maintains this project but wanted to get some 👀 on this PR
cc @kentcdodds @MichaelDeBoey @NicholasBoll
I'm not sure I'm in favor of this change. This is one of those situations where you're letting the compiler lie to you. I would much rather you add a type guard (instanceof) or a cast (as), than hide that away in an abstraction.
I'm not sure I'm in favor of this change. This is one of those situations where you're letting the compiler lie to you. I would much rather you add a type guard (
instanceof) or a cast (as), than hide that away in an abstraction.
Yea I'm glad you called it out. I was following the pattern in Cypress itself but actual type guards would be useful. Let me consider this more.
It's also the same way we define it in DOM Testing Library: https://github.com/testing-library/dom-testing-library/blob/main/types/queries.d.ts#L5
Adding type guards as far as I can tell will require an API change to all the queries, something like this looks appealing: https://effectivetypescript.com/2020/07/27/safe-queryselector/
Still researching but haven't found many great examples in the wild, maybe because it's sort of straightforward?