Date picker Error

Date picker Error

Hello all supporter,

I have the problems related to the use of date picker.
the below is my code:

<script type="text/javascript" src="~/Scripts/jquery.ui.datepicker-fr.js"></script>
    <% ScriptManager.RegisterStartupScript(this, this.GetType(), "scripts", "onload();", true); %>
    <script language="javascript" type="text/javascript">
        $(document).ready(function () {
         
            onload();
        });

        function onload() {
           
            //alert("MessageBox");
            $(".TbDateRPL").datepicker();
            $(".DateAppelOpport").datepicker();
            $("#opportAccordion").accordion({ autoHeight: false });
        }
    </script>
but when i run it it got error, and put the status "TypeError: $(...).datepicker is not a function"
could u clarify me what is the problem of that?

Thank you