How do I use jQuery to disable a form's submit button until every required field has been filled?

Question

I have a form with multiple inputs, select boxes, and a textarea. I would like to have the submit button be disabled until all of the fields that I designate as required are

Answer 1

Here's something comprehensive, just because:

$(document).ready(function() {
    $form = $('#formid'); // cache
    $form.find(':input[type="submit"]').prop('disabled', true); // disable submit btn
    $form.find(':input').change(function() { // monitor all inputs for changes
        var disable = false;
        $form.find(':input').not('[type="submit"]').each(function(i, el) { // test all inputs for values
            if ($.trim(el.value) === '') {
                disable = true; // disable submit if any of them are still blank
            }
        });
        $form.find(':input[type="submit"]').prop('disabled', disable);
    });
});

http://jsfiddle.net/mblase75/xtPhk/1/