How to calculate height of viewable area (i.e., window height minus address & bookmark bars) in mobile Safari for web app?

Question

What is the right way to calculate how much viewable space is available on mobile Safari? By viewing area, we mean the amount of the screen actually available to a web app,

Answer 1

For anyone who comes in 2020, window.screen.availHeight is the only one that works as @Marcel Falliere's comment below.