JSFiddle - React, Tailwind, and code Playground

HTML

<div id="event"></div>

JavaScript

$(function(){
    
    window['hasFocus'] = false;
    
    $(window)
        .bind('focus', function(ev){
            window.hasFocus = true;
            $('#event').append('<div>'+(new Date()).getTime()+' focus</div>');
        })
        .bind('blur', function(ev){
            window.hasFocus = false;
            $('#event').append('<div>'+(new Date()).getTime()+' blur</div>');
        })
        .trigger('focus');
    
    setInterval(function() {
        $('#event').append('<div>'+(new Date()).getTime()+' has focus '+(window.hasFocus ? 'yes' : 'no')+'</div>');
    }, 1000);
});