html:

<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>表单示例</title>
</head>
<body>
    <!-- 创建表单 -->
    <form action="form.php" method="post" id="myForm">
        <!-- 普通文字输入框 -->
        <label for="normalText">普通文字:</label>
        <input type="text" id="normalText" name="normalText" value="请输入普通文字"><br><br>
        
        <label for="picture">图片<label>
        <input type="file" single accept=".png,.jpg" id="pictureAddr" name="pictureAddr"><br><br>

        <!-- 用户名输入框 -->
        <label for="username">用户名:</label>
        <input type="text" id="username" name="username"><br><br>

        <!-- 密码输入框 -->
        <label for="password">密码:</label>
        <input type="password" id="password" name="password"><br><br>

        <!-- 提交按钮 -->
        <input type="submit" value="提交">
    </form>

    <script type="text/javascript">
	    var fileUP = document.getElementById('pictureAddr');
	    var myForm = document.getElementById('myForm');
        //拦截表单的submit事件, 然后根据自己的逻辑选择提交
	    myForm.addEventListener('submit', function(e) {
	        e.preventDefault();
	        if (fileUP.value == null || fileUP.value == '') {
	            console.log('图片不能为空');
	        } else {
		        console.log(fileUP.value);
		        this.submit();
	        }
	    });
        //监听input文件选择的变化
	    fileUP.addEventListener('change', function(e) {
	        console.log(e.target.files);
	        if (e.target.files.length == 0)
                return;
	        var t_file = e.target.files[0];
	        if (t_file.name.indexOf('jpg')!=-1 || t_file.name.indexOf('png')!=-1) {
		        console.log('是图片');
	        } else {
		        console.log('文件类型错误');
		        fileUP.value = null;
	        }
	    }, false);
    </script>
</body>
</html>

form.php:

<?php
// 设置默认字符集为UTF-8
header('Content-Type: text/html; charset=utf-8');

// 检查是否提交了表单
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    // 获取用户输入的用户名和密码
    $username = $_POST['username'];
    $password = $_POST['password'];
    // 验证用户名和密码是否正确(这里仅作示例,实际应用中需要连接数据库进行验证)
    if ($username == "admin" && $password == "123456") {
	    echo '登录成功'. "<br>";
    }
}
?>
01-06 10:52