The read-only valueMissing property of a ValidityState object indicates if a required control, such as an <input>, <select>, or <textarea>, has an empty value.

If the required attribute is set, and no <option> is selected or a <textarea> or user-editable <input> is empty, the valueMissing property will be true. The property is only true if the field is required and has no value; if the field is not required, or if the field is required and has a value, the value is false.

• Constraint validation
• Forms: Data form validation
• Regular Expressions