JSFiddle - React, Tailwind, and code Playground

HTML

Currently <b id="status">without</b> focus...

JavaScript

function check()
{
    if(document.hasFocus() == lastFocusStatus) return;
    
    lastFocusStatus = !lastFocusStatus;
    statusEl.innerText = lastFocusStatus ? 'with' : 'without';
}

window.statusEl = document.getElementById('status');
window.lastFocusStatus = document.hasFocus();

check();
setInterval(check, 200);