javascript SaveAs for Excel

Question

我有以下内容：

var oWin = window.open("about:blank", "_blank");
oWin.document.write(strExcelHtml);
oWin.document.close();
var success = oWin.document.execCommand('SaveAs', false, fileName)
oWin.close();

当保存窗口出现时，我希望将.xls视为＆＃34;另存为＆＃34;类型。我该怎么做？