Testing selector speed

Steve Souders' aforementioned tests use JavaScript’s new Date(). However, nowadays, modern browsers (iOS/Safari were a notable exception at the time of testing) support the Navigation Timing API (https://www.w3.org/TR/navigation-timing/) which gives us a more accurate measure we can use. For the tests, I implemented it like this:

<script>
    ;(function TimeThisMother() {
        window.onload = function(){
            setTimeout(function(){
            var t = performance.timing;
                alert("Speed of selection is: " + (t.loadEventEnd - t.responseEnd) + " milliseconds");
            }, 0);
        };
    })();
</script>

This lets us limit the timing of the tests between the point all assets have been received (responseEnd) and the point the page is rendered (loadEventEnd).

So, I set up a very simple test. 20 different pages, all with an identical, enormous DOM, made up of 1000 identical chunks of this markup...