How do you send an ajax request every time that a form input field changes?

Question

For example, there is an input field. Every time a user types a key into that field, it sends an AJAX request with whatever text is currently in that input, and does something

Answer 1

$('#yourInputId').keyup (function () {
    $.post('http://yoururl.com', { value: $(this).val() }).done(function (data) {
        $('#feedbackDivId').html(data);
    });
});