Force user to fill all fields before enabling form submit

Question

I have a form containing various fields.

See jsFiddle demo.

My aim is to enable the submit button only when the user has filled in all fields.

So far,

Answer 1

Thought I might chip in. Assuming as little as possible.

jQuery("input, textarea").on("keyup click", function () { // going vanilla after easy-mode attach
    var sub = document.getElementById('subnewtide');
    if (require_all(find_form(this))) {
        sub.removeAttribute('disabled');
        sub.disabled = false;
    } else {
        sub.setAttribute('disabled', 'disabled');
        sub.disabled = true;
    }
});

function concat(a, b) { // concating Array-likes produces Array
    var slice = [].slice; // not assuming Array.prototype access
    return [].concat.call(
        slice.call(a, 0),
        slice.call(b, 0)
    );
}

function find_form(e) { // shim input.form
    if (e) do {
        if (e.tagName === 'FORM') return e;
    } while (e = e.parentNode);
    return null;
}

function require_all(form, dontIgnoreHidden) { // looks at textareas & inputs (excluding buttons)
    var inp = concat(form.getElementsByTagName('input'), form.getElementsByTagName('textarea')),
        rad = {}, // not assuming Object.create
        i, j,
        has = {}.hasOwnProperty; // not assuming Object.prototype access
    for (i = 0; i < inp.length; ++i) {
        switch ((inp[i].type || '').toLowerCase()) {
            default: // treat unknown like texts
            case 'text':
                if (!inp[i].value) return false; break;
            case 'checkbox':
                if (!inp[i].checked) return false; break;
            case 'radio':
                j = inp[i].getAttribute('name');
                if (!rad[j]) rad[j] = inp[i].checked;
                break;
            case 'hidden':
                if (dontIgnoreHidden && !inp[i].value) return false; break;
            case 'button':
            case 'submit':
                break;
        }
    }
    for (j in rad) if (!has || has.call(rad, j)) // not assuming hasOwnProperty
        if (!rad[j]) return false;
    return true;
}