readableStreamDefaultReader.cancel([reason])

• reason <any>

• 返回：undefined 兑现的 promise。

  ¥Returns: A promise fulfilled with undefined.

取消 <ReadableStream> 并返回一个在基础流被取消时完成的 promise。

¥Cancels the <ReadableStream> and returns a promise that is fulfilled when the underlying stream has been canceled.