var url = 'data:application/octet-stream,' + encodeURIComponent('This is test message!%');
                var anchor = document.createElement('a');
                anchor.setAttribute('href', url);
                anchor.setAttribute('download', 'test.txt');

                if (document.createEvent) {
                    var e = window.document.createEvent("MouseEvents");
                    e.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
                    anchor.dispatchEvent(e);
                } else if (document.createEventObject) {
                    try {
                        document.body.appendChild(anchor);
                        var clickEvent = document.createEventObject();
                        anchor.fireEvent('onclick', clickEvent); // <-- there is error "Unspecified error"
                        document.body.removeChild(anchor);

                    } catch (ex) {
                        alert(ex);
                    }
                }