Measure page scroll speed

measure-page-scroll-speed.js

// Measure page scroll speed
(function() {
    if (document.body.scrollHeight <= window.innerHeight) {
        console.log('Scrolling measurement is only possible if the window can actually be scrolled!');
        return;
    }

    function calcScrollTime(startTime, iterations) {
        return Math.round((Date.now() - startTime) / iterations) / 1000;
    }

    var MAX_ITERATIONS = 3,
        startTime = Date.now(),
        iterationStartTime = startTime,
        iteration = MAX_ITERATIONS,
        y = 0,
        step = 10,
        timer = setInterval(function() {
            y += step;
            if (y < document.body.scrollHeight && y >= 0) {
                window.scrollTo(0, y);
            } else if (--iteration) {
                console.log('Scroll ' + (MAX_ITERATIONS - iteration) + ': ' + calcScrollTime(iterationStartTime, 1) + 's');
                iterationStartTime = Date.now();
                // scroll in reverse direction
                step = -step;
            } else {
                clearInterval(timer);
                console.log('It takes approximately ' + calcScrollTime(startTime, 3) + ' seconds to scroll this document');
            }
        }, 0);
})();