Format date in yy-mm-dd

Question

<script>
    var $j = jQuery.noConflict();

    $j(document).ready(function() {
        $j("#date").datepicker({
            format: 'yyyy-mm-dd'
        });

        $j("#date").on("change", function () {
            var fromdate = $j(this).val();
            alert(fromdate);
        });
    });
</script>

I want to format date in yy-mm-dd. Its not working for me . where i am going wrong any idea?

Thanks in advance