I don't event use event classes from haxe-react x)
Should I update and pull https://github.com/kLabz/haxe-react-types/blob/master/src/react/types/event/SyntheticEvent.hx here?

SyntheticEvent is also used in react native but no DOM stuff there

I think both implementation are similar. But iirc at runtime SyntheticEvent is actually a "class" instead of a plain anon object. And I think both target and nativeEvent should be parametrized without constraints. Because in react-native I have encountered cases that target is always null/undefined and nativeEvent can be a plain object.