Populate dropdown from SharePoint Site (JSOM)

markup.html

<select name="departmentDD" title="department" id="departmentDD" onchange="populateDeapartment(this.value)">

populatedropdown.js

function populateDeapartment(selectedValue) {
    $('#DeapartmentDD option').each(function () {
        if ($(this).val() != '0') {
            $(this).remove();
        }

        $.ajax({
            cache: false,
            url: "my-url/_api/web/lists/GetByTitle('Deapartment')/items?$select=Title,Deapartment&$filter=Title eq '" + selectedValue + "'",
            type: 'GET',
            dataType: 'json',
            async: false,
            headers: {
                "accept": "application/json;odata=verbose;charset=utf-8"
            },
            success: function (data) {
                $.each(data.d.results, function (i, result) {
                    ItemDeapartmentDD = result.Deapartment;
                    $('#DeapartmentDD').append("<option value='" + ItemDeapartmentDD + "'>" + ItemDeapartmentDD + "</option>");
                });

            }, //end of success
            error: function ajaxError(response) {
                alert(response.status + ' ' + response.statusText);
            },

        }); //end of ajax

    }); //end of each
} //end of function