FocusIn/FocusOut for relatedTarget in IE

[vankop]

Currently (react <=16.0.0) there is no support for FocusIn/FocusOut events. But the problem is that in IE <= 11 blur event has no relatedTarget, so it will be great to support such events.

So, the question is will be such support in later versions?
This problem was mentioned in #3751, but there is no answer.

[jquense]

It's not likely there will be support unfortunately, Microsoft isn't gonna fix it for ie11 and there is really no way to effectively work around it in the event system (I have tried!).

The best way I've found to handle this, depending on your use case, is to listen for both blur and focus in a container with a set timeout and coordinate between the two events

[vankop]

@jquense You are totaly correct. Also there is fix using focusin/focusout out of react lifecycle. For example, using addEventListener/removeEventListener in componentDidMount/componentWillUnmount.

However, you will stuck with testing using common react test tools, react can't simulate unsupported events