<form action="../json/data.json" name="my-form">
    <div data-formjs-question class="form-group">
        <div class="answers-box label-move-up">
            <input name="name" type="text" data-length="[3,20]" class="form-control" required />
            <label>Name</label>
        </div>
        <div class="field-error-message small"></div>
    </div>
    <div data-formjs-question class="form-group">
        <div class="answers-box label-move-up">
            <input name="surname" type="text" data-length="[3,20]" class="form-control" data-validate-if-filled />
            <label>Surname</label>
        </div>
        <div class="field-error-message small"></div>
    </div>
    <div data-formjs-question class="form-group">
        <div class="answers-box label-move-up">
            <input name="email" type="email" class="form-control" required />
            <label>Email</label>
        </div>
        <div class="field-error-message small"></div>
    </div>
    <div data-formjs-question class="form-group">
        <p class="mb-2 small">Select your contact preferences <br />( 2 answers max )</p>
        <div class="answers-box">
            <div class="form-check">
                <input name="contactPrefCheck" type="checkbox" value="sms" class="form-check-input" id="checkbox-1-a" required data-checks="[1,2]" />
                <label class="form-check-label" for="checkbox-1-a">SMS</label>
            </div>
            <div class="form-check">
                <input name="contactPrefCheck" type="checkbox" value="email" class="form-check-input" id="checkbox-2-a" required />
                <label class="form-check-label" for="checkbox-2-a">Email</label>
            </div>
            <div class="form-check">
                <input name="contactPrefCheck" type="checkbox" value="app-notiifcation" class="form-check-input" id="checkbox-3-a" required />
                <label class="form-check-label" for="checkbox-3-a">App Notification</label>
            </div>
        </div>
        <div class="field-error-message small"></div>
    </div>
    <div data-formjs-question class="form-group">
        <div class="answers-box">
            <div class="small">
                I agree with the <a href="#" target="_blank">Privacy Policy</a>.
            </div>
            <div class="form-check form-check-inline">
                <input class="form-check-input" type="radio" name="privacyCheck" id="privacyCheck-1-a" value="accepted" required />
                <label class="form-check-label" for="privacyCheck-1-a">Yes</label>
            </div>
            <div class="form-check form-check-inline">
                <input class="form-check-input" type="radio" name="privacyCheck" id="privacyCheck-2-a" value="" required />
                <label class="form-check-label" for="privacyCheck-2-a">No</label>
            </div>
        </div>
        <div class="field-error-message small"></div>
    </div>
    <div class="text-center">
        <button type="submit" class="btn btn-light">SEND</button>
    </div>
    <div class="d-none alert mt-5 mb-4" role="alert" data-formjs-global-feedback></div>
</form>

function onValidationDemoErrorsJs ( obj, options ){
    const isValid = obj.result,
          $field = obj.$field,
          $container = $field.closest('[data-formjs-question]');

    if( $container !== null && !options.fieldOptions.skipUIfeedback ){
        if( isValid ){

            // REMOVE ERRORS FROM PAGE
            $container.querySelector('.field-error-message').innerHTML = '';

        } else {

            // PRINT ERRORS AS FOR obj.errors
            if( obj.errors ){
                let errorsHTML = '';

                if( obj.errors.empty ){
                    errorsHTML += '<p>This field cannot be empty</p>';
                } else {
                    for(let errorName in obj.errors){
                        if( errorName !== 'rule' ){
                            const printError = errorName.replace(/([A-Z])/g, function(all, letter){
                                    return ' ' + letter.toLowerCase();
                                });
                            errorsHTML += '<li>Error: '+ printError +'</li>';
                        }
                    }
                    errorsHTML = 'This field is not valid:<ul>' + errorsHTML + '</ul>';
                }

                $container.querySelector('.field-error-message').innerHTML = errorsHTML;
            }

        }
    }
}

const $form = document.querySelector('form');

$form.addEventListener('fjs.field:validation', function(event){
    onValidationDemoErrorsJs( event.detail, this.formjs.options );
});

const formInstance = new Form( $form );