The closed read-only property of the ReadableStreamBYOBReader interface returns a Promise that fulfills when the stream closes, or rejects if the stream throws an error or the reader's lock is released.

This property enables you to write code that responds to an end to the streaming process.

A Promise.

The code below shows the pattern for handling the closed/error state of a BYOBReader.

const reader = stream.getReader({ mode: "byob" });
reader.closed
  .then(() => {
    // Resolved - code to handle stream closing
  })
  .catch(() => {
    // Rejected - code to handle error
  });

• ReadableStreamBYOBReader() constructor
• Using readable byte stream