var getTop = document.getElementById("get-top");
var head = document.getElementById("head");
getTop.onclick = function () {
    var time = setInterval(function () {
        document.body.scrollTop = document.body.scrollTop - 50;
        if (document.body.scrollTop === 0) {
            clearInterval(time);
        }
    }, 1);
};
链接:https://segmentfault.com/q/1010000003855799原文:http://www.cnblogs.com/pengchengzhong/p/6023986.html