Yunkou

function smoothScroll(el, to, duration) {
    if (duration < 0) {
        return;
    }
    var difference = to - $(window).scrollTop();
    var perTick = difference / duration * 10;
    this.scrollToTimerCache = setTimeout(function() {
        if (!isNaN(parseInt(perTick, 10))) {
            window.scrollTo(0, $(window).scrollTop() + perTick);
            smoothScroll(el, to, duration - 10);