bug: useLocation may break your app because of mounted pages

[FernetB]

Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Ionic Framework Version

v5.x

Current Behavior

If you have 3 pages A, B and C

You go from A -> B with a stateB and then B -> C with stateC the app may crash because when you are on page C, B is mounted and the stateB that returns the useLocation hook, will have the stateC value because you are no longer on B

This is a silly example of an app crashing with this:

https://codesandbox.io/s/holy-waterfall-t9ofg1?file=/src/pages/UserDetailPage/UserDetailPage.tsx

Expected Behavior

Each page should have their useLocation not muting with the new state.

I know that this is not a bug per se, but a bad interaction between useLocation and Ionic with mounted pages.

But is something that needs to be cared about and or offer a solution, or clariy in the documentation

Steps to Reproduce

Easy example:
1 -Click in any User
2 - Then click on More details button
3 - app break
https://codesandbox.io/s/holy-waterfall-t9ofg1?file=/src/pages/UserDetailPage/UserDetailPage.tsx

Code Reproduction URL

https://codesandbox.io/s/holy-waterfall-t9ofg1?file=/src/pages/UserDetailPage/UserDetailPage.tsx

Ionic Info

Ionic:

Ionic CLI
Ionic Framework : @ionic/react 5.9.1

Capacitor:

Capacitor CLI : 4.1.0
@capacitor/android : 4.1.0
@capacitor/core : 4.1.0
@capacitor/ios : 4.1.0

Utility:

cordova-res : 0.15.1
native-run : 1.7.0

System:

NodeJS : v14.17.0
npm : 6.14.13
OS : Windows 10

Additional Information

No response

[liamdebeasi]

Thanks for filing the follow-up issue. So in this case, you're going to need to add an undefined check on person before accessing dni:

dni: {location.state?.person?.dni} <br />

It's certainly not an ideal experience, but it is the intended behavior of inactive pages. We need to keep those pages around in the DOM to a) preserve component state and b) allow for swipe to go back on iOS. This is an experience we are looking to improve, but at the moment this is recommendation for developers.

[FernetB]

Yes, thats fixes the issue, but the main problem is mostly that noone will know of that until they have it.

Would be nice if ionic has a useIonLocation that will be something like useIonLocation<Person> = useLocation<Partial<Person>>

That on top of that you will be able to add some logic if you want.

[liamdebeasi]

Yes, thats fixes the issue, but the main problem is mostly that noone will know of that until they have it.

In that case, it sounds like we should clarify this behavior on the documentation. If you have some thoughts on how we can better explain this, we'd be happy to review a PR. It might be good to place the information in https://github.com/ionic-team/ionic-docs/edit/main/docs/react/lifecycle.md.

[FernetB]

There you have it!

ionic-team/ionic-docs#2894

[liamdebeasi]

Thanks for the contribution! I merged your PR in ionic-team/ionic-docs#2894. I am going to close this, but let me know if you have questions.