Javascript DOM oninvalid Event via HTML Tag oninvalid attribute

Introduction

If you click submit, without filling out the text field, an alert message will occur.

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<!DOCTYPE html>
<html>
<body>

<p id="demo"></p>
<script>
function test(){//from  w  ww  .  j  av a  2s .com
   document.getElementById("demo").innerHTML = "You must fill out the form!";
}
</script>
<form action="/action_page.php" method="get">
  Name: <input type="text" 
  oninvalid="test();" name="fname" required>
  <input type="submit" value="Submit">
</form>
</body>
</html>

Bubbles:	No
Cancelable:	Yes
Event type:	Event
Supported HTML tags:	<input>

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