//右侧返回顶部

function myEvent(obj, ev, fn) {
    if (obj.attachEvent) {
        obj.attachEvent('on' + ev, fn);
    } else {
        obj.addEventListener(ev, fn, false);
    }
}
myEvent(window, 'load', function () {
    var oRTT = document.getElementById('gotop');
    var pH = document.documentElement.clientHeight;
    var timer = null;
    var scrollTop;
    window.onscroll = function () {
        scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
        if (scrollTop >= pH) {
            oRTT.style.visibility = 'visible';
        } else {
            oRTT.style.visibility = 'hidden';
        }
        return scrollTop;
    };
    oRTT.onclick = function () {
        clearInterval(timer);
        timer = setInterval(function () {
            var now = scrollTop;
            var speed = (0 - now) / 10;
            speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);
            if (scrollTop == 0) {
                clearInterval(timer);
            }
            document.documentElement.scrollTop = scrollTop + speed;
            document.body.scrollTop = scrollTop + speed;
        }, 30);
    }
});