1 var $this = $('.container-scroll'),
2 $goup = $('.goup'),
3 //元素可视区的高度
4 offtop = $(window).height() - $this.offset().top,
5 isscroll =false;
6 //监听滚动事件 控制 回到顶部按钮出现
7 $this.on('scroll',function () {
8 var rolltop = $this.scrollTop();
9 if ( rolltop > offtop) {
10 $goup.css({'opacity':.5,'bottom':40+'px'});
11 }else if(rolltop < offtop){
12 $goup.css({'opacity':.5,'bottom':-40+'px'});
13 }
14 });
15
16 $goup.on('click',function () {
17 isscroll =true;
18 gotop();
19 });
20
21 $this.on('touchstart',function () {
22 isscroll = false;
23 });
24
25
26 function gotop(){
27 var y = Math.max(0,$this.scrollTop());
28 var speed = 1.2;
29 $this.scrollTop( Math.floor(y / speed));
30 if (isscroll && $this.scrollTop() > 0) {
31 var timer= setTimeout(gotop, 10);
32 }else if(!isscroll){
33 clearTimeout(timer);
34 }
35 }
