HTML DOM insertBefore() Methodw3schools链接haveatry

w3schools链接
 have a try

<!DOCTYPE html>
<html>
<body>

<ul id="myList">
  <li>Coffee</li>
  <li>Tea</li>
</ul>

<p>Click the button to insert an item to the list.</p>

<button onclick="myFunction()">Try it</button>

<p><strong>Example explained:</strong><br>First create a LI node,<br> then create a Text node,<br> then append the Text node to the LI node.<br>Finally insert the LI node before the first child node in the list.</p>

<script>
function myFunction() {
    var newItem = document.createElement("LI");//创一个新的li
    var textnode = document.createTextNode("Water");//创一个文本节点放内容
    newItem.appendChild(textnode);//把文本节点添加到li里面

    var list = document.getElementById("myList");//从html中得到list
    list.insertBefore(newItem, list.childNodes[0]);//把刚才创建的li插入list中，位置自己定
    /*list.insertBefore(newItem,list.childNodes[list.childNodes]);
    list.insertBefore(newItem,list.childNodes[list.childNodes.length]);
    list.appendChild(newItem)
    这三句都可以在list最后插入节点*/
}
</script>

</body>
</html>