add __v and __o keys to the custom handler to support Preact

[dios-david]

Hi there,

I'm using preact and I noticed this console warning in my browser:
react-fast-compare cannot handle circular refs

After a bit of investigation I found out that one of my dependencies is using react-fast-compare which would work fine with preact as well after a minor modification.
Instead of forking the project (e.g. preact-fast-compare) I thought it would be better to contribute to the project and make it work with both frameworks.

[developit]

Strong +1 from the Preact core team on this!

A suggestion: perhaps it would be worth ignoring all properties that have leading _? It'd be a more widespread change, but would also be a nice way to allow hiding properties from comparison that doesn't require defining them as non-enumerable.

[dios-david]

Yeah that sounds reasonable, I'm happy to make those changes if needed. I leave the decision up to the maintainers. @chrisbolin

[chrisbolin]

alright, current quick thoughts...

• the code change would be minimal
• the support change would be a little more. we'd have to make sure we support future versions of preact and adopt their release cadence
• we should probably have tests for preact as well

[chrisbolin]

oh also... i'm nervous about ignoring all _-prefixed properties: this could both be a regression for existing users AND cause new users some pain and confusion.

[chrisbolin]

just thinking ahead: when this is finished we should release as a minor version. I don't think it warrants a major release

[kale-stew]

Merging this into a feature branch so we can move forward with polishing up new Preact tests separate from your work, @dios-david. Thanks for introducing this feature. 🙌