Web Serial API: how to flush and get length of data in buffer?

Question

Is it possible to test whether data is available in the input stream (port.readable)?
And how can it be flushed (read until ...? cancel() a reader?)?

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Docs:

• https://web.dev/serial/ -> https://developer.chrome.com/articles/serial/
• https://developer.mozilla.org/en-US/docs/Web/API/Web_Serial_API
  • https://developer.mozilla.org/en-US/docs/Web/API/SerialPort
  • https://developer.mozilla.org/en-US/docs/Web/API/Serial