Detect fullscreen mode

Question

Modern desktop version of IE 10 is always fullscreen.

There is a living specification for :fullscreen pseudo-class on W3

But when I tried to det

Answer 1

Reading MDN Web docs, I like this native method.

https://developer.mozilla.org/en-US/docs/Web/API/DocumentOrShadowRoot/fullscreenElement

function is_fullscreen(){
    return document.fullscreenElement != null;
}

or fancier

let is_fullscreen = () => !! document.fullscreenElement

This method also works when you open developer tools in browser. Because fullscreen is applied to a particular element, null means none of it is in fullscreen.

You can even extend to check a particular element eg:

function is_fullscreen(element=null){
    return element != null? document.fullscreenElement == element:document.fullscreenElement != null;
}

Which only return true if currently is fullscreen and (element is null or element is the fullscreened element)