/Web APIs

WebTransport: createUnidirectionalStream() method

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

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

The createUnidirectionalStream() method of the WebTransport interface opens a unidirectional stream; it returns a WritableStream object that can be used to reliably write data to the server.

"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.

Note: This feature is available in Web Workers





Return value

A WritableStream object.


InvalidStateError DOMException

Thrown if createUnidirectionalStream() is invoked while the WebTransport is closed or failed.


Use the createUnidirectionalStream() method to get a reference to a WritableStream. From this you can get a writer to allow data to be written to the stream and sent to the server.

Use the close() method of the resulting WritableStreamDefaultWriter to close the associated HTTP/3 connection. The browser tries to send all pending data before actually closing the associated connection.

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

  try {
    await writer.close();
    console.log("All data has been sent.");
  } catch (error) {
    console.error(`An error occurred: ${error}`);

You can also use WritableStreamDefaultWriter.abort() to abruptly terminate the stream. When using abort(), the browser may discard any pending data that hasn't yet been sent.

// ...

const stream = await transport.createUnidirectionalStream();
const writer = ws.getWriter();

// ...

await writer.abort();
// Not all the data may have been written.


Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
createUnidirectionalStream 97 97 No No 83 No 97 97 No 68 No 18.0
byob_readers 109 109 No No 95 No 109 109 No 74 No No

See also

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