let asFileSystemHandle: WebAPI.FileAPI.fileSystemFileHandle => WebAPI.FileAPI.fileSystemHandle
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let createWritable: ( WebAPI.FileAPI.fileSystemFileHandle, ~options: WebAPI.FileAPI.fileSystemCreateWritableOptions=?,) => promise<WebAPI.FileAPI.fileSystemWritableFileStream>
let getFile: WebAPI.FileAPI.fileSystemFileHandle => promise< WebAPI.FileAPI.file,>
let isSameEntry: ( WebAPI.FileAPI.fileSystemFileHandle, WebAPI.FileAPI.fileSystemHandle,) => promise<bool>