The Opera onfocus, onblur bug demonstrator

// ==UserScript==
// @name            The Opera onfocus, onblur bug demonstrator
// @include         http://example.com/


let focusCounter = 1;
let blurCounter  = 1;

window.onfocus = () => {
    logEntry(`<p style="color: #FFA400">FOCUS: ${blurCounter}</p>`);
    focusCounter++;
};

window.onblur  = () => {
    logEntry(`<p style="color: #1049A9">BLUR: ${blurCounter}</p>`);
    blurCounter++;
};


resetHTML();
window.addEventListener("click", () => { logEntry("<hr>"); }, true);




function logEntry(entry) {
    document.querySelector("#log")
            .insertAdjacentHTML("beforeend", entry);
}


function resetHTML() {
    document.body.innerHTML = "";
    document.querySelector("body")
            .insertAdjacentHTML("afterbegin", `<div id="log"></div>`);
    document.querySelector("body > div")
            .insertAdjacentHTML("afterbegin", `<a href="http://example.com/">New window</a>`);

    document.querySelector("#log").addEventListener("click", resetHTML, false);

    focusCounter = 1;
    blurCounter  = 1;
}