js实现数字滚动特效

let numchange = function (){
  let point = '.'
  // 数字容器高度
  let height = 60
  // 每次滚动距离/滚动速度
  let p = 3
  // 数字spanclass
  let spanClass = 't-num-s'
  // 数字divclass
  let divClass = 't-num'
//
  let cache = {}
  function createDiv(id, num, len, paddingNum){
    let str = ''
    for (let i = 0; i < len; i++) {
      str += `
${paddingNum === undefined?num[i]:paddingNum}
`
    }
    return str
  }
  function initZero(id, count){
    document.getElementById(id).innerHTML = createDiv(id,null,count,0)
  }
  function refresh(oldNum, newNum, id){
    let len = newNum.length - oldNum.length;
    for (let i = 0; i < len; i++) {
      oldNum.unshift('0')
    }
    document.getElementById(id).innerHTML = createDiv(id,oldNum,oldNum.length)
  }
  function refresh2(oldNum, newNum, id){
    let len = oldNum.length - newNum.length;
    for (let i = 0; i < len; i++) {
      oldNum.shift()
    }
    document.getElementById(id).innerHTML = createDiv(id,oldNum,oldNum.length)
  }
  function scrollNum(id, num, order){
    let h = num * height
    let e = document.getElementById(id)
    let t = setInterval(() => {
      let m = e.scrollTop;
      m = m + p
      if(m > h){
        clearInterval(t)
        let cs = e.children
        for (let i = cs.length-2; i >= 0; i--) {
          e.removeChild(cs[i])
        }
        return
      }
      e.scrollTop = m
    }, 10)
  }
  function createSpan(num){
    let span = document.createElement('span')
    span.className = spanClass
    span.innerText = num
    return span
  }
  function appendNum(id, start, end){
    let f = document.createDocumentFragment()
    let count = 0
    if(start === end && isNaN(start)){
      return 0
    }
    if(isNaN(start) && !isNaN(end)){
      for (let i = 0; i <= end; i++) {
        f.appendChild(createSpan(i))
        count++
      }
      document.getElementById(id).appendChild(f)
      return count
    }
    if(!isNaN(start) && isNaN(end)){
      for (let i = start+1; i <= 9; i++) {
        f.appendChild(createSpan(i))
        count++
      }
      f.appendChild(createSpan('.'))
      count++
      document.getElementById(id).appendChild(f)
      return count
    }
    if(start < end){
      for (let i = start+1; i <= end; i++) {
        f.appendChild(createSpan(i))
        count++
      }
    }else if(start > end){
      for (let i = start+1; i <= 9; i++) {
        f.appendChild(createSpan(i))
        count++
      }
      for (let i = 0; i <= end; i++) {
        f.appendChild(createSpan(i))
        count++
      }
    }else{
      return 0
    }
    document.getElementById(id).appendChild(f)
    return count
  }
 
  /**
   * @param id 容器id
   * @param num 展示的数字
   */
  function change(id, num){
    console.log(num)
    let strArr = num.toString().split('');
    let oldNum = cache[id]
    // 如果没有缓存，开始数字全部填充0
    if(!oldNum){
      initZero(id,strArr.length)
      oldNum = []
    }else{
      oldNum = cache[id].toString().split('')
      // 如果新数字长，原来数字左侧填充0
      if(oldNum.length < strArr.length){
        refresh(oldNum, strArr, id)
        // 如果新数字短，原来数字左侧移除
      }else if(oldNum.length > strArr.length){
        refresh2(oldNum, strArr, id)
      }
    }
    // 循环比较每个数字差异，添加需要滚动的数字列
    for (let i = 0, len = strArr.length; i < len; i++) {
      let start = oldNum[i] !== point ? parseInt(oldNum[i]||0) : oldNum[i]
      let end = strArr[i] !== point ? parseInt(strArr[i]||0) : strArr[i]
      let count = appendNum(id+i, start, end)
      if(count > 0){
        // 数字滚动
        scrollNum(id+i, count, i+1)
      }
    }
    cache[id] = num
  }
 
  function config(param){
    if(param.p){
      p = param.p
    }
    if(param.height){
      height = param.height
    }
    if(param.spanClass){
      spanClass = param.spanClass
    }
    if(param.divClass){
      divClass = param.divClass
    }
    return scroll
  }
 
  let scroll = {
    change: change,
    config: config
  }
  return scroll
}