<html>
<head>
</head>
<body>
<div id='timing_hidden' class='tab'>
<ul id="ul">
<li index="0">item1</li>
<li index="1">item2</li>
<li index="2">item3</li>
<li index="3">item4</li>
</ul>
</div>
</body>
<script>
var datas= ["item1","item2","item3","item4"];
function SetTop(idx){
var lis = document.getElementById("ul").children;
debugger;
for (let index = 0; index < lis.length; index++) {
if(idx==index){
const element = lis[index];
element.remove();
document.getElementById("ul").prepend(element);
}
}
}
SetTop(2);
</script>
</html>