Mastering HTML5 Forms

Constraint validations

The algorithm that browsers run to determine the validity of a form when it is submitted is called constraint validation. To constrain data or check validity, the algorithm utilizes new HTML5 attributes such as min, max, step, pattern, and required, as well as existing attributes such as maxlength and type.

In HTML5, basic constraints are declared in two different ways:

• By choosing the most semantically appropriate value for the type attribute of the <input> element
• By setting values on validation-related attributes and allowing basic constraints to be described in a simple way without the need for JavaScript

HTML5 constraint validation APIs

Nowadays, an increasing number of browsers are supporting the constraint validation API, ...