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1.通过PHP语句判断 ：
html中内容:
<form action="submit.php" method="post"> <textarea name="text"></textarea> </form>
php中内容:
//submit.php <?php if(isset($_POST['text']) && strlen(trim($_POST['text']))>0) echo '不空'; else echo '空 '; ?>
2.通过JS语句判断
<html> <head> <title>JS判断input是否为空</title> <script>function op(){ if(document.getElementById("ip").value==""){ alert("input为空"); }else{ alert(document.getElementById("ip").value); } } </script> </head> <body> <input id="ip" onblur="op()" value="JS"/> </body> </html>
3.通过required属性判断
<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>表单</title> </head> <body> <form action="" style="display: grid;" method="POST"> <div> <label for="username">账号：</label> <input type="text" id="username" required> <!--required为必须填写数据--> </div> </body> </html>
推荐：《html知识》
