Page({
 data: {
  topNum: 0
 },

 returnTop: function () {
  this.setData({
   topNum: this.data.topNum = 0
  });
 }
}) 

<scroll-view scroll-y scroll-with-animation='true' scroll-top='{{ topNum }}'>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
 <view>1</view>
</scroll-view>

<view class='top' catchtap='returnTop'>顶部</view>

page{
 width: 100%;
 height: 100%;
}

scroll-view{
 height: 100%;
 width: 100%;
}

view{
 width: 100%;
 height: 200px;
 text-align: center;
 line-height: 200px;
 font-weight: 600;
}

view:nth-child(odd){
 background-color: red;
}

.top{
 width: 50px;
 height: 50px;
 position: fixed;
 right: 10px;
 bottom: 10px;
 z-index: 1;
 background-color: yellow;
 color: red;
 text-align: center;
 line-height: 50px;
}