files/en-us/web/api/readablebytestreamcontroller/byobrequest/index.md
{{APIRef("Streams")}}{{AvailableInWorkers}}
The byobRequest read-only property of the {{domxref("ReadableByteStreamController")}} interface returns the current BYOB request, or null if there are no pending requests.
An underlying byte source should check this property, and use it to write data to the stream if it exists (rather than using {{domxref("ReadableByteStreamController.enqueue()")}}). This will result in an efficient zero-byte transfer of the data to the consumer.
A {{domxref("ReadableStreamBYOBRequest")}} object instance, or null.
The example in Using readable byte streams > Creating a readable socket push byte stream shows how you use a byobRequest to transfer data (if it exists), or otherwise copy the data to the stream's internal queues using {{domxref("ReadableByteStreamController.enqueue()")}}.
The relevant code is reproduced below.
If the byobRequest exists, data is read into {{domxref("ReadableStreamBYOBRequest.view","controller.byobRequest.view")}}, and then {{domxref("ReadableStreamBYOBRequest.respond()")}} is called to signal the amount of data that is ready to transfer.
if (controller.byobRequest) {
const v = controller.byobRequest.view;
bytesRead = socket.readInto(v.buffer, v.byteOffset, v.byteLength);
if (bytesRead === 0) {
controller.close();
}
controller.byobRequest.respond(bytesRead);
} else {
// Write to data using enqueue().
}
{{Specifications}}
{{Compat}}