jquery - change form action when event

Question

I have auto-complate code that fill the text field and also fill hidden field with the row ID I would like that when the ID field is not empty than the form ACTION will change to another url. Again - the contactID field is something that automatically get filled

HTML

<form method="post" action="index.php?page=contacts" class="quick_search">
                    <input type="text" name="fNameHe" value="<?PHP echo $_POST['fNameHe'] ?>"  />
                    <input type="hidden" name="contactID" value="" id="contactID" />
                    <span id="ajax_response_contact" class='ajax_response'></span>

JS:

$("#contactID").on('change keyup copy paste cut', function() {  // <- not working

    var contactID = $( "#contactID" ).val();
    alert(contactID);
    var action = $(this).val() != "" ? "contactPage=contactID="+contactID : "contacts";
    $("#contactID").parents('form').attr("action", action);
});