JSFiddle - React, Tailwind, and code Playground

JavaScript

function focusin() { document.title="BLURRED"; }
function focusout() { document.title="FOCUSED"; }

if ("onfocusin" in document)
    document.onfocusin = focusin,
    document.onfocusout = focusout;
else
    window.onblur = focousout,
    window.onfocus= focusin;