.rollCon {
 position: fixed;
 top: 0;
 left: 0;
 width: 100%;
 height: 60rpx;
 z-index: 100;
 background: #fde8c7;
 font-size: 20rpx;
 line-height: 60rpx;
}
 
.box {
 width: 100%;
 position: relative;
}
 
.text {
 white-space: nowrap;
 position: absolute;
 top: 0;
 font-size: 24px;
}

Page({
 
 /**
  * 页面的初始数据
  */
 data: {
  interval: null,
  text: '995年JavaScript诞生时如早一年',
  pace: 1.2, //滚动速度
  interval: 20, //时间间隔
  size: 24, //字体大小in px
  length: 0, //字体宽度
  offsetLeft: 0, //
  windowWidth: 0,
 },
 //根据viewId查询view的宽度
 queryViewWidth: function(viewId) {
  //创建节点选择器
  return new Promise(function(resolve) {
   var query = wx.createSelectorQuery();
   var that = this;
   query.select('.' + viewId).boundingClientRect(function(rect) {
    resolve(rect.width);
   }).exec();
  });
 
 },
 //停止跑马灯
 stopMarquee: function() {
  var that = this;
  //清除旧的定时器
  if (that.data != null) {
   clearInterval(that.interval);
  }
 },
 //执行跑马灯动画
 excuseAnimation: function() {
  var that = this;
  if (that.data.length > that.data.windowWidth) {
   //设置循环
   let interval = setInterval(function() {
    if (that.data.offsetLeft <= 0) {
     if (that.data.offsetLeft >= -that.data.length) {
      that.setData({
       offsetLeft: that.data.offsetLeft - that.data.pace,
      })
     } else {
      that.setData({
       offsetLeft: that.data.windowWidth,
      })
     }
    } else {
     that.setData({
      offsetLeft: that.data.offsetLeft - that.data.pace,
     })
    }
   }, that.data.interval);
  }
 },
 //开始跑马灯
 startMarquee: function() {
  var that = this;
  that.stopMarquee();
  //初始化数据
  that.data.windowWidth = wx.getSystemInfoSync().windowWidth;
  that.queryViewWidth('text').then(function(resolve) {
   that.data.length = resolve;
   console.log(that.data.length + "/" + that.data.windowWidth);
   that.excuseAnimation();
  });
 }
 })