js indexOf 列表筛选

先来一堆效果图：
代码：
<!DOCTYPE html>
<html>

    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="user-scalable=no,width=360,initial-scale=1,minimum-scale=1,maximum-scale=1">
        <title></title>
        <style type="text/css">
            body{
                margin: 0;
            }
            #myInput {
                background-image: url('https://static.runoob.com/images/mix/searchicon.png');
                /* 搜索按钮 */
                background-position: 10px 12px;
                /* 定位搜索按钮 */
                background-repeat: no-repeat;
                /* 不重复图片*/
                 100%;
                font-size: 16px;
                /* 加大字体 */
                padding: 12px 20px 12px 40px;
                border: 1px solid #ddd;
                margin-bottom: 12px;
            }
            
            #myUL {
                /* 移除默认的列表样式 */
                list-style-type: none;
                padding: 0;
                margin: 0;
            }
            
            #myUL li a {
                border: 1px solid #ddd;
                /* 链接添加边框 */
                margin-top: -1px;
                background-color: #f6f6f6;
                padding: 12px;
                text-decoration: none;
                font-size: 18px;
                color: black;
                display: block;
            }
            
            #myUL li a.header {
                background-color: #e2e2e2;
                cursor: default;
            }
            
            #myUL li a:hover:not(.header) {
                background-color: #eee;
            }
        </style>
    </head>

    <body>
        <input type="text" id="myInput" onkeyup="myFunction()" placeholder="搜索...">

        <ul id="myUL">
            <li>
                <a href="#" class="header">A</a>
            </li>
            <li>
                <a href="#">Adele</a>
            </li>
            <li>
                <a href="#">Agnes</a>
            </li>

            <li>
                <a href="#" class="header">B</a>
            </li>
            <li>
                <a href="#">Billy</a>
            </li>
            <li>
                <a href="#">Bob</a>
            </li>
            <li>
                <a href="#">博客</a>
            </li>


            <li>
                <a href="#" class="header">C</a>
            </li>
            <li>
                <a href="#">Calvin</a>
            </li>
            <li>
                <a href="#">Christina</a>
            </li>
            <li>
                <a href="#">Cindy</a>
            </li>
        </ul>
    </body>

</html>
<script type="text/javascript">
    function myFunction() {
        // 声明变量
        var input, filter, ul, li, a, i;
        input = document.getElementById('myInput');
        filter = input.value.toUpperCase();
        ul = document.getElementById("myUL");
        li = ul.getElementsByTagName('li');

        // 循环所有列表，查找匹配项
        for(i = 0; i < li.length; i++) {
            a = li[i].getElementsByTagName("a")[0];
            if(a.innerHTML.toUpperCase().indexOf(filter) > -1) {
                li[i].style.display = "";
            } else {
                li[i].style.display = "none"; 
            }
        }
    }
</script>