WebTransport: supportsReliableOnly static property

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 supportsReliableOnly static read-only property of the WebTransport interface returns a boolean value that indicates whether the browser supports WebTransport sessions over exclusively reliable transports, such as HTTP/2. Such sessions can't send unreliable datagrams, which need HTTP/3 over QUIC.

Value

A boolean value: true if the browser supports reliable-only WebTransport sessions, false otherwise.

Examples

Basic usage

const url = "https://example.com:4999/webtransport";

async function connect() {
  // WebTransport itself may be unavailable, so check before reading the static property
  if (typeof WebTransport === "undefined") {
    console.log("WebTransport is not supported in this browser.");
    return;
  }

  // Without reliable-only support, the session needs HTTP/3,
  // so it fails on networks that block UDP
  if (!WebTransport.supportsReliableOnly) {
    console.log("This browser can't fall back to a reliable-only session.");
  }

  const transport = new WebTransport(url);

  try {
    await transport.ready;
    console.log("Connected");
  } catch (error) {
    console.error("Connection failed:", error);
  }
}

connect();