$(document).ready(function() {
    var required = $('.required');
    
    if(required.size()) {
        var form = required.parents('form:first');
        form.submit(function() {
            return document.validate.check();
        });    
    }
});

document.validate = {
    check : function() {
        var validated = true;
        $(':input.required').each(function() {
            if(!$(this).val()) {
                validated = false;
                $('label[for="'+ $(this).attr('id') +'"]').addClass('invalid');
            } else $('label[for="'+ $(this).attr('id') +'"]').removeClass('invalid');
        });
        
        return validated;
    }
}