Currently I am using this code to read the entries in a FileSystemEntry object:

  function readEntries(entry: FileSystemEntry): Promise<FileSystemEntry[]> {
    return new Promise((resolve, reject) => {
      var reader: FileSystemDirectoryReader = entry.createReader();
      reader.readEntries(function (entries) {
        resolve(entries);
      });
    });
  }

However, TypeScript detects all these "bugs" (even though it works perfectly):

And Mozilla Developer Network claims: Experimental. Expect behavior to change in the future. 2

How can an API be experimental and already deprecated at the same time and what should be the alternative?