jellesn on "Contact Form 7 - jQuery checkbox"

$(document).ready(function() {

        //Hide the field initially
        $("#hide3").hide(); 

        //Show the text field only when the third option is chosen - this doesn't
        $('#nieuwsbrief').change(function() {
                if ($("#nieuwsbrief").val() == "Ja") {
                        $("#hide3").show();
                }
                else {
                        $("#hide3").hide();
                }
        });

});

[checkbox* nieuwsbrief id:nieuwsbrief "Ja"]

<div class="hide" id="hide3">
[email email]
</div>

How to get this working? With select it works perfectly..