relatedTarget missing from focus and blur events

[jondkoon]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
When using handlers for onFocus and onBlur the relatedTarget property is missing from event.nativeEvent

If the current behavior is a bug, please provide the steps to reproduce:
Checkout this glitch: https://glitch.com/edit/#!/rnw-relatedtarget-bug

• Tab through the buttons and observe that the relatedTarget is undefined when the event is normalized by react-native-web (check the console output)

What is the expected behavior?

• event.nativeEvent.relatedTarget would be set for focus events.
  It looks like this property is also set on some mouse events: https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/relatedTarget

Environment (include versions). Did this work in previous versions?
It looks like the issue was introduced with this commit: b4e4bfb#diff-e1a663dbcbd141f6fa72d76ecc2260ac

• React Native for Web (version): 0.5.1
• React (version): 16.2

[necolas]

I don't think it's part of the React Native API so I'm curious what you need it for

[jondkoon]

We might be able to work around it. @sidhu663 should have some thoughts.

[sidhu663]

We're currently using this for focus management. We keep track of the focusable nodes within a modal and if the relatedTarget on a blur is outside the focusable set, we know that it's a focusout. I don't believe React Native has an onFocusOut since onBlur bubbles so I'm not sure how it could be determined whether the blur will result in a focus loss or not without the related target.

Maybe it's possible to use document.activeElement but it seems that the body has focus during the blur phase before the focus on the target happens which we can't capture within a component

[necolas]

Perhaps you could look into doing this outside of React / React Native? That's how this library juggles some focus related tasks that need to happen out of tree, and it's how PlayStation implemented controls for focus-based UIs with RNW. Also worth noting that OSS focus traps don't rely on relatedTarget https://github.com/davidtheclark/focus-trap

[jondkoon]

Thanks for the info. I'll look into working around this today.

[necolas]

Any follow up?

[jondkoon]

We worked around it by using addEventListener in the ref callback. Thanks for taking a look!

[necolas]

Ok