W3School TIY Editor
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<!DOCTYPE html> <html> <body> <form action="/demo/htmldom/action_page.php"> 名字：<input type="text" id="myText" name="fname"> <input type="submit"> </form> <p>单击“试一试”按钮可为文本字段设置 required 属性。</p> <p><b>提示：</b>请在点击“试一试”按钮前后点击“提交”按钮，查看效果。</p> <button onclick="myFunction()">试一试</button> <p id="demo"></p> <script> function myFunction() { document.getElementById("myText").required = true; document.getElementById("demo").innerHTML = "The required property was set. The text field must now be filled out before submitting the form."; } </script> </body> </html>