Get the height of a div without Jquery

This:

or this:

are exactly my problem.
Except that the first solution uses jquery to get the height.
And the second one hides the pages during transitions, which kills the purpose of a slidebox.

Again, the problem is that if I have 3 slides, each with unknown height (can't be defined with css thus), they will all take the height of the biggest slide. (because the whole ion-slide-box will take the biggest height)