WebTransport: incomingBidirectionalStreams property

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Note: This feature is available in Web Workers.

The incomingBidirectionalStreams read-only property of the WebTransport interface represents one or more bidirectional streams opened by the server. Returns a ReadableStream of WebTransportBidirectionalStream objects. Each one can be used to reliably read data from the server and write data back to it.

"Reliable" means that transmission and order of data are guaranteed. This provides slower delivery (albeit faster than with WebSockets) than datagrams, but is needed in situations where reliability and ordering are important, like chat applications.



An initial function is used to read the WebTransportBidirectionalStream objects from the ReadableStream. For each one, the WebTransportBidirectionalStream.readable and WebTransportBidirectionalStream.writable values are passed to other functions to read from and write to those streams.

async function receiveBidirectional() {
  const bds = transport.incomingBidirectionalStreams;
  const reader = bds.getReader();
  while (true) {
    const { done, value } = await reader.read();
    if (done) {
    // value is an instance of WebTransportBidirectionalStream
    await readData(value.readable);
    await writeData(value.writable);

async function readData(readable) {
  const reader = readable.getReader();
  while (true) {
    const { value, done } = await reader.read();
    if (done) {
    // value is a Uint8Array.

async function writeData(writable) {
  const writer = writable.getWriter();
  const data1 = new Uint8Array([65, 66, 67]);
  const data2 = new Uint8Array([68, 69, 70]);


# dom-webtransport-incomingbidirectionalstreams

Browser compatibility

BCD tables only load in the browser

See also