Improve error message when duplicate keys are detected (in __DEV__)

[SDRACK]

Reproduction

https://formkit.link/4920b90204eb2a0437e463b81dc5e938

Describe the bug

This is a funny one - if an ID is added to a mask input in a repeater, when items are added they break.

I've not checked other input types, but it might apply beyond masks.

To replicate in the playground:

1. at first, everything works as expected
2. add a new item to the repeater
3. the new item doesn't respect the mask nor populate the form data

In my opinion, this is a question of messaging more than anything else. Duplicated IDs are a bad thing so shouldn't be used, but the current situation of unexplained errors makes debugging the problem very difficult.

Would it be possible to add a console error / warning if IDs are added to repeaters, in order to make this a trivial fix?

Environment

• OS: Mac OS 14.5 (23F79)
• Browser: Chrome Version 125.0.6422.141
• Version: Formkit 1.6

[justin-schroeder]

Ids must always be globally unique (that's just an HTML thing).

[SDRACK]

Ids must always be globally unique (that's just an HTML thing).

Yeah, agree @justin-schroeder - my concern is around the visibility of the issue. It's a pretty straightforward mistake to make, but the error that occurs in FormKit is very unclear - things just stop working.

Would it be possible to add a Javascript error / warning if someone does this to explain what's happened, rather than have fields just fail as in the playground example?

[justin-schroeder]

That seems like a reasonable thing to do. In general we try to not put too much additional weight into the bundle to guard for error messages, but we recently added a development build and I think we could improve the error messages that are displayed at development time. I’ll rename this issue to that effect.