Validation in HTML5. :invalid classe after submit

Question

I\'m building a form and I want to use the :invalid selector to give the \"required\" input fields a red border if the user presses submit without filling them, but

Answer 1

for 'required' validation

way 1 - set 'required' attribute for each element on form submit

// submit button event
$('#form-submit-btn').click(function(event) {
    // set required attribute for each element
    $('#elm1, #elm2').attr('required','true');

    // since required attribute were not set (before this event), prevent form submission
    if(!$('#form')[0].checkValidity())
        return;

    // submit form if form is valid
    $('#form').submit();

});

way 2 - use 'data' attribute