console 命令行工具 X clear
console
<!DOCTYPE html> 
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script>
        window.onload = function () 
        {
            var oBtn = document.getElementById("btn");
            var oUl = document.getElementById("list");
            oBtn.onclick = function () 
            {
                var preElement = oUl.children[2].previousElementSibling;
                oUl.removeChild(preElement);
            };
        }
    </script>
</head>
<body>
    <ul id="list">
        <li>HTML</li>
        <li>CSS</li>
        <li>JavaScript</li>
        <li>jQuery</li>
        <li>Vue.js</li>
    </ul>
    <input id="btn" type="button" value="删除" />
</body>
</html>