Ajax can't force a file to download?

Question

JavaScript

Good afternoon!
Project in Yii2. I want to generate a csv file and make it download.
If you go to the method through the browser line: the file is generated and even downloaded. Here is the method itself:

public function actionExportStaffCsv() {
        //$requestID = htmlspecialchars(trim(Yii::$app->request->get('dept')));
        $filepath = $_SERVER["DOCUMENT_ROOT"].'/web/junk/test_'.date('dmYhis').'.csv';
        $output = fopen($filepath, 'w+');
        fputcsv($output, ["#", "Description", "test", "test2"], ';');
        fputcsv($output, ["1","2","3","4"], ';');
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename='.'test.csv');
        header('Content-Length: ' . filesize($filepath));
        readfile($filepath);
    }

But if you access the method through Ajax, the file is generated but not downloaded. Here is the jquery:

$("#exportStaffCsv").on('click', function (e) {
        e.preventDefault();
        //var last_element = getUrlParam();
        $.ajax({
            url: "/ru/tree/export-staff-csv",
            data: {dept: 4},
            success: function (resp) {
                //alert(resp);
            }
        });
    });

Answer 1

In response to ajax, return the url to the file and already in js process the server response, redirecting the user to the received url