留言板案例

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>留言板案例</title>
</head>
<body>
    <style>
        div {
            width: 300px;
            height: 500px;
            border: 3px solid black;
            display: grid;
            grid-template-rows: 1fr 30px;
            background-color: green;
        }
            div > input{
               background-color: rgb(71, 37, 174);
            }
            li  {
                list-style: none;
                border: 1px solid red;
                margin: 5px;
            }
    </style>
    <div>
    <ul class="test">
    </ul>
    <input type="text" onkeydown="insertComment(this)" placeholder="请输入留言" autofocus>
</div>
    <script>
        const insertComment = function(ele){
            // 按下回车键提交
            if(event.key === 'Enter'){
                // 非空判断
                if(ele.value.length === 0){
                    alert('消息不能为空')
                    // 重置焦点
                    ele.focus()
                    // 直接返回
                    return false 
                }
        const ul = document.querySelector('.test');
        ul.insertAdjacentHTML('beforeend', `<li>${ele.value}</li>`);
        ele.value = null 
            }
        }
    </script>
</body>
</html>
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