New in HTML5.

<input required>

Attribute of
<input> HTML Tag
What does <input required> do?
Specifies that the input field is required; disallows form submission and alerts the user if the required field is empty.

Code Example

 <p><i>Try submitting without filling in the field.</i></p>
 <label for="animal">What is your favorite animal?</label><br>
 <input name="animal" id="animal" value="" required><br>
 <input type="submit" >

Try submitting without filling in the field.

required and data validation

As with all HTML5 in-browser data validation, required should primarily be seen as a UI helper. A malicious user can easily submit a form request that includes or excludes whatever data they want. Data validation and sanitization need to occur on the server, once the data is received.

This is the mysterious user account for the admin.

Browser Support for required

1045139 (with problems)9.6