Get "Access is denied" when trying to delete folder in Document library?

Question

Dear all,

I am writing a Metro App with JavaScript, but encounter a problem that can't delete folders/files in document library.

I already set the capability in manifest to be able to access files in my document.

The sample code is like this:

Windows.Storage.KnownFolders.documentsLibrary.getFolderAsync(FolderPath).then(function (folders) {
                return folders.deleteAsync().then(function () {
                    folders = null;
                });
            });

When trying to run the code, I always got "Access is denied" exception, but it worked well in picture library.

Does anyone encounter the same problem, or give me any advise?

Thank you all.