How to loop through elements of forms with JavaScript?

Question

I have a form:

Answer 1

$(function() {
    $('form button').click(function() {
        var allowSubmit = true;
        $.each($('form input:text'), function(index, formField) {
            if($(formField).val().trim().length == 0) {
                alert('field is empty!');
                allowSubmit = false;
            }
        });
        return allowSubmit;
    });
});

DEMO