Function read_as_data_url

pub fn read_as_data_url<F>(blob: &Blob, callback: F) -> FileReader
where
    F: FnOnce(Result<String, FileReadError>) + 'static,

Asynchronously converts the blob into a base64 encoded data: URL and then passes it to the callback.

If the returned FileReader is dropped before the callback is called, the read will be cancelled.