How do i know if the editor is rendered side-by-side or unified?

[diddiman]

When creating the editor i know i can set the render mode to be side-by-side, all that works fine. I can also toggle to unified, which also works.

However, by default when the width gets down under certain level the editor will auto switch from side-by-side to unified, is it possible to listen to some event or something is i always know which mode the editor is in?