Javascript怎么实现字幕滚动

<p class="scroll">
    <span>这里是要现实的滚动内容......</span>
 </p>

.scroll {
  width: 400px;
  height: 23px;
  white-space: nowrap;
  overflow: hidden;
  margin-left: 40px;
  position: relative;
}
.scroll > span {
  position: absolute;
}

// 字幕滚动变量
var scrollTime = null
var LEN = 400 // 一个完整滚动条的长度
var x = 0
// 启动滚动定时器
function roll () {
  console.log('启动')
  var tag1 = document.querySelector('.scroll>span')
  var tag2 = tag1.nextSibling
  var fun = function () {
    tag1.style.left = x + 'px'
    tag2.style.left = (x + LEN) + 'px'
    x = x - 5
    if ((x + LEN) === 0) {
      x = 0
    }
  }
  if (scrollTime) {
    clearInterval(scrollTime)
  }
  scrollTime = setInterval(fun, 300)
}
// 绑定鼠标事件
function bindMouseEvent () {
  var el = document.querySelector('.scroll>span')
  var el2 = el.cloneNode(true)
  LEN = el.clientWidth + 100 // 动态修改滚动条的长度，避免文字过多重叠
  el2.style.left = (x + LEN) + 'px'
  el.parentElement.appendChild(el2)
  el.addEventListener('mouseenter', function (e) {
    clearInterval(scrollTime)
  })
  el.addEventListener('mouseleave', function (e) {
    roll()
  })
}