W3School TIY Editor
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<!DOCTYPE html> <html> <body> <form action="/demo/html/action_page.php" method="get"> Name: <input type="text" id="myInput" name="fname" pattern=".{6,}" required> <input type="submit" value="Submit"> </form> <p>If you submit the form with less than 6 characters, an alert message will occur.</p> <p><b>注释：</b>Internet Explorer 9 及更早版本或 Safari 不支持 oninvalid 事件。</p> <script> document.getElementById("myInput").addEventListener("invalid", myFunction); function myFunction() { alert("Must contain 6 or more characters"); } </script> </body> </html>