Page load time counter in JS

What I would like to see on websites is a little counter of the page load time placed in the footer, so I decided to share you the little piece of code in order to easily integrate this counter in your website footer.

ES5 Version (Older browsers)

(function () {
    var time = window.performance && performance.timing;
    if (time) {
        var load = (time.loadEventEnd - time.navigationStart) / 1e3;
        alert("This page loaded in " + load + " seconds");
    }
})();

ES6 Version (Modern browsers)

(() => {
    const time = window.performance && performance.timing;
    if (time) {
        const load = (time.loadEventEnd - time.navigationStart) / 1e3;
        alert(`This page loaded in ${load} seconds`)
    }
})();