[javascript] $(...).datepicker is not a function - JQuery - Bootstrap

I'm trying to include the datepicker for Bootstrap but am getting the following error:

Uncaught TypeError: $(...).datepicker is not a function

I don't see why it's there. I've looked at other cases of this error, but none match mine.

HTML:

<script src="https://code.jquery.com/jquery-2.2.4.min.js" integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44=" crossorigin="anonymous"></script>
<script src="<?php echo BASE_URL; ?>/js/moment.min.js"></script>
<script src="<?php echo BASE_URL; ?>/js/bootstrap.min.js"></script>
<script src="<?php echo BASE_URL; ?>/js/bootstrap-datetimepicker.min.js"></script>
<script src="<?php echo BASE_URL; ?>/js/main.js"></script>

<div class="col-md-6">
    <div class="form-group">
         <label for="geboortedatum">Geboortedatum:</label>
         <div class="input-group datepicker" data-provide="datepicker">
               <input type="text" name="geboortedatum" id="geboortedatum" class="form-control">
               <div class="input-group-addon">
                   <span class="glyphicon glyphicon-th"></span>
               </div>
         </div>
    </div>
</div>

JS:

$(document).ready(function() {

    $('.datepicker').datepicker({
        format: 'dd/mm/yyyy'
    });
});

UPDATE after adding JQuery UI

It now looks like the following:

Need to include jquery-ui too:

<script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>

To get rid of the bad looking datepicker you need to add jquery-ui css

<link rel="stylesheet" type="text/css" href="https://code.jquery.com/ui/1.12.0/themes/smoothness/jquery-ui.css">

You need to include jQueryUI

$(document).ready(function() {_x000D_
_x000D_
    $('.datepicker').datepicker({_x000D_
        format: 'dd/mm/yyyy'_x000D_
    });_x000D_
});

<script src="https://code.jquery.com/jquery-2.2.4.min.js" integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44=" crossorigin="anonymous"></script>_x000D_
<script   src="https://code.jquery.com/ui/1.11.3/jquery-ui.min.js"   integrity="sha256-xI/qyl9vpwWFOXz7+x/9WkG5j/SVnSw21viy8fWwbeE="   crossorigin="anonymous"></script>_x000D_
<script src="<?php echo BASE_URL; ?>/js/moment.min.js"></script>_x000D_
<script src="<?php echo BASE_URL; ?>/js/bootstrap.min.js"></script>_x000D_
<script src="<?php echo BASE_URL; ?>/js/bootstrap-datetimepicker.min.js"></script>_x000D_
<script src="<?php echo BASE_URL; ?>/js/main.js"></script>_x000D_
_x000D_
<div class="col-md-6">_x000D_
    <div class="form-group">_x000D_
         <label for="geboortedatum">Geboortedatum:</label>_x000D_
         <div class="input-group datepicker" data-provide="datepicker">_x000D_
               <input type="text" name="geboortedatum" id="geboortedatum" class="form-control">_x000D_
               <div class="input-group-addon">_x000D_
                   <span class="glyphicon glyphicon-th"></span>_x000D_
               </div>_x000D_
         </div>_x000D_
    </div>_x000D_
</div>

You can try the following and it worked for me.

Import following scripts and css files as there are used by the date picker.

<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.4.1/js/bootstrap-datepicker.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.4.1/css/bootstrap-datepicker3.css"/>
<link rel="stylesheet" href="css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="http://code.jquery.com/ui/1.11.0/jquery-ui.js"></script>
<link rel="stylesheet" href="http://code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">

The JS coding for the Date Picker I use.

<script>
        $(document).ready(function(){
            // alert ('Cliecked');
            var date_input=$('input[name="orangeDateOfBirthForm"]'); //our date input has the name "date"
            var container=$('.bootstrap-iso form').length>0 ? $('.bootstrap-iso form').parent() : "body";
            var options={
                format: 'dd/mm/yyyy', //format of the date
                container: container,
                changeYear: true, // you can change the year as you need
                changeMonth: true, // you can change the months as you need
                todayHighlight: true,
                autoclose: true,
                yearRange: "1930:2100" // the starting to end of year range 
            };
            date_input.datepicker(options);
        });
    </script>

The HTML Coding:

 <input type="text" id="orangeDateOfBirthForm" name="orangeDateOfBirthForm" class="form-control validate" required>
 <label data-error="wrong" data-success="right" for="orangeForm-email">Date of Birth</label>

I resolved this by arranging the order in which your JS is being loaded.

You need to have it as jQuery -> datePicker -> Init js

Call your JQuery in your header, datePicker script in head below your jquery and Init JS in footer

 <script type="text/javascript">

    var options={
            format: 'mm/dd/yyyy',
            todayHighlight: true,
            autoclose: true,
        };

    $('#datetimepicker').datepicker(options);

</script>

I had similiar problem. The quick fix I found is to change:

<div class="input-group datepicker" data-provide="datepicker">

to

<div class="input-group date" data-provide="datepicker">