ACF action "acf/input/admin_footer" not working with get_field_objects()

acf-dave.php

<?php
function dave_acf_code_master_footer() {
    $id = get_the_ID();
    $field = get_field_object( 'code_type', $id );
    $field_label = esc_attr( 'acf-' . $field['key'] );
?>
<script type="text/javascript">
    jQuery( document ).ready( function() {
        function setEditorCodeType() {
            var editor = ace.edit( jQuery(".editor")[0] );
            editor.session.setMode( "ace/mode/" + jQuery("<?= $field_label; ?>").val() );
        }
        jQuery("<?= $field_label; ?>").change( function() { setEditorCodeType(); });
        setEditorCodeType();
    });
</script>
<?php
}
add_action( 'acf/input/admin_footer', 'dave_acf_code_master_footer' );

So get_field_objects() returns an empty value if you are creating a new post. But it works if you are editing an existing post...

So how do I get the field key when creating a new post?