Function use_active_element 

pub fn use_active_element() -> OptionLocalSignal<Element>

Reactive document.activeElement

Demo

Link to Demo

Usage

let active_element = use_active_element();

Effect::new(move || {
    log!("focus changed to {:?}", active_element.get());
});

Server-Side Rendering

Make sure you follow the instructions in Server-Side Rendering.

On the server this returns a Signal that always contains the value None.