javascript select options by ajax

selectAjax.js

<script>
function onCodeChanged() {
    var select = document.getElementById('category');
    var value = select.options[select.selectedIndex].value;
    var text = select.options[select.selectedIndex].text + '선택';
    $.ajax({
        type: "POST"
        , url: "url"
        , data: "category=" + value
        , success: function (response) {
            var optionToAdd = function (code, label) {
                var opt = document.createElement('option')
                opt.value = code
                opt.text = label
                return opt
            }
            var code = document.getElementById('code');
            while (code.options.length > 0) {
                code.remove(0);
            }
            code.add(optionToAdd(null, text), null)

            response.forEach(
                    function (value, index, ar) {
                        code.add(optionToAdd(value.code, value.label), null)
                    }
            )

            code = null
            optionToAdd = null
            response = null
        }
    });
    select = null
    value = null
}
</script>