addEventListener support for Reader

Couldn't the reader returned by getReader() implement the FileReader interface or is there another way to "track" reader progress outside a while loop?

var { message } = await openpgp.encrypt({
        message: openpgp.message.fromBinary((new File([], "foo.txt")).stream()),
        publicKeys: [KEYS],
        armor: false
    }),
_reader = openpgp.stream.getReader(message.packets.write());
_reader.addEventListener('progress', event => console.log(`${event.type}: ${event.loaded} bytes transferred`));

Start at the getReader entry point used by openpgp.stream.getReader(message.packets.write()) and compare the requested addEventListener('progress') behavior with the FileReader interface. Determine what progress information the reader can expose and define completion by demonstrating progress tracking outside the while loop.