valueMissing property

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.