JavaScript实现前端密码框实时长度验证与提示

<!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>密码框输入提示</title>
    <style>
        div {
            width: 600px;
            margin: 100px auto;
        }
        
        input {
            outline: none;
        }
        
        .message {
            display: inline-block;
            font-size: 12px;
            color: #999;
            background: url(images/提示.png) no-repeat left center/16px 16px;
            padding-left: 20px;
        }
        
        .wrong {
            background-image: url(images/错误.png);
            color: red;
        }
        
        .right {
            background-image: url(images/正确.png);
            color: green;
        }
    </style>
</head>

<body>
    <div class="register">
        <input type="password" class="inp">
        <p class="message">请输入8~18位密码</p>
    </div>
    <script>
        var password = document.querySelector('.inp');
        var message = document.querySelector('.message');

        password.onblur = function() {
            if (this.value.length < 8 || this.value.length > 18) {
                message.innerHTML = '密码长度错误，应为8~18位';
                message.className = 'message wrong';
            } else {
                message.innerHTML = '密码长度正确';
                message.className = 'message right';
            }
        }
    </script>
</body>

</html>