1 function backTop(btnId) {
2 var btn = document.getElementById(btnId);
3 var d = document.documentElement;
4 var b = document.body;
5 window.onscroll = set;
6 btn.style.display = "none";
7 btn.onclick = function() {
8 btn.style.display = "none";
9 window.onscroll = null;
10 this.timer = setInterval(function() {
11 d.scrollTop -= Math.ceil((d.scrollTop + b.scrollTop) * 0.1);
12 b.scrollTop -= Math.ceil((d.scrollTop + b.scrollTop) * 0.1);
13 if ((d.scrollTop + b.scrollTop) == 0) clearInterval(btn.timer, window.onscroll = set);
14 },
15 10);
16 };
17 function set() {
18 btn.style.display = (d.scrollTop + b.scrollTop > 100) ? 'block': "none"
19 }
20 };
21 backTop('goTop');