HTML oninvalid Attribute

<form action="action.php">
	Name: <input type="text" oninvalid="alert('You must enter this field!');" name="fname" required>
	<input type="submit" value="Submit">
</form>

Meaning

The oninvalid attribute fires when a submittable element do not satisfy their constraints during form validation.

Standard Syntax

<element oninvalid="script">

Browser Support

Status

Applies to:

The oninvalid attribute can be used on the following element:

Attribute Values