x
<html><body><form action="https://www.w3schools.com/action_page.php" method="get"> Name: <input type="text" id="myInput" name="fname" required> <input type="submit" value="Submit"></form><p>If you click submit, without filling out the text field,an alert message will occur.</p><p><strong>Note:</strong> The oninvalid event is not supported in Internet Explorer 9 and earlier.</p><script>document.getElementById("myInput").addEventListener("invalid", myFunction);function myFunction() { alert("You must fill out the form!");}</script></body><!-- Mirrored from www.w3schools.com/jsref/tryit.asp?filename=tryjsref_oninvalid_addeventlistener by HTTrack Website Copier/3.x [XR&CO'2014], Wed, 21 Dec 2022 17:39:59 GMT --></html>