The datagrams read-only property of the WebTransport interface returns a WebTransportDatagramDuplexStream instance that can be used to send and receive datagrams — unreliable data transmission.

"Unreliable" means that transmission of data is not guaranteed, nor is arrival in a specific order. This is fine in some situations and provides very fast delivery. For example, you might want to transmit regular game state updates where each message supersedes the last one that arrives, and order is not important.

A WebTransportDatagramDuplexStream object.

The WebTransportDatagramDuplexStream.writable property returns a WritableStream object that you can write data to using a writer, for transmission to the server:

const writer = transport.datagrams.writable.getWriter();
const data1 = new Uint8Array([65, 66, 67]);
const data2 = new Uint8Array([68, 69, 70]);
writer.write(data1);
writer.write(data2);

The WebTransportDatagramDuplexStream.readable property returns a ReadableStream object that you can use to receive data from the server:

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

• Using WebTransport
• WebSockets API
• Streams API
• WebTransport over HTTP/3