<ul class="list" id="list"> <li class="in">1</li> <li class="in">2</li> <li class="in">3</li> <li class="in">4</li> <li class="in">5</li> <li class="in">6</li>  </ul>

.in{ height: 20px; line-height: 20px; width: 20px; background-color: blue; text-align: center; color: white;}

var oList = document.getElementById('list');//新增一個li元素var oAdd = document.createElement('li');//設置新增元素的css樣式oAdd.className = "in";oAdd.style.cssText = 'background-color:red;border-radius:50%';//添加到oList中oList.insertBefore(oAdd,null);var num = -1;var max = oList.children.length;function incrementNumber(){ num++; //oList.getElementsByTagName('li')[max]相當于null，所以不報錯 oList.insertBefore(oAdd,oList.getElementsByTagName('li')[num]);  if(num == max){  num = -1; }  if(num == 0){  num = 1; } setTimeout(incrementNumber,1000);}setTimeout(incrementNumber,1000);