用javascript方式做skydrive接口开发，如何做上传下载功能？

Question

function downloadFile_onClick() {
    var picker = setupSavePicker();
    picker.pickSaveFileAsync().then(
        function (file) {
            if (file && (file instanceof Windows.Storage.StorageFile)) {
                WL.backgroundDownload({
                    path: "file.8c8ce076ca27823f.8C8CE076CA27823F!129/picture?type=thumbnail",
                    file_output: file
                }).then(
                    function (response) {
                        document.getElementById("infoLabel").innerText = "Downloaded file.";
                    },
                    function (responseFailed) {
                        document.getElementById("infoLabel").innerText =
                            "Error calling API: " + responseFailed.error.message;
                    }
                );
            }
            else {
                document.getElementById("infoLabel").innerText = "Cannot download file.";
            }
        },
        function (fileFailed) {
            document.getElementById("infoLabel").innerText = "Cannot download file.";
        }
    );
}

function setupSavePicker() {
    var savepicker = new Windows.Storage.Pickers.FileSavePicker();
    savepicker.suggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.documentsLibrary;
    savepicker.fileTypeChoices.insert("Picture", [".jpg"]);
    return savepicker;
}
上面是官网API的例子，但是运行的时候报错  "Windows未定义"，不知怎么解决，上传下载功能如何实现呢？求帮助，谢谢