WritableStreamDefaultWriter: свойство ready

function sendMessage(message, writableStream) {
  // defaultWriter is of type WritableStreamDefaultWriter
  const defaultWriter = writableStream.getWriter();
  const encoder = new TextEncoder();
  const encoded = encoder.encode(message);
  encoded.forEach((chunk) => {
    // Make sure the stream and its writer are able to
    //   receive data.
    defaultWriter.ready
      .then(() => defaultWriter.write(chunk))
      .then(() => {
        console.log("Chunk written to sink.");
      })
      .catch((err) => {
        console.error(`Chunk error: ${err}`);
      });
    // Call ready again to ensure that all chunks are written
    //   before closing the writer.
    defaultWriter.ready
      .then(() => defaultWriter.close())
      .then(() => {
        console.log("All chunks written");
      })
      .catch((err) => {
        console.error(`Stream error: ${err}`);
      });
  });
}