WebTransport: ready property

Baseline 2026

Newly available

Since March 2026, this feature works across the latest devices and browser versions. This feature might not work in older devices or 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 ready read-only property of the WebTransport interface returns a promise that resolves when the transport is ready to use.

This promise is created when the WebTransport object is created and is resolved when a connection is established. Accessing or awaiting this promise does not trigger any action; it only allows actions to be taken when the transport is ready, similar to listening to an event.

Value

A Promise that resolves to undefined.

Examples

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

async function initTransport(url) {
  // Initialize transport connection
  const transport = new WebTransport(url);

  // The connection can be used once ready fulfills
  await transport.ready;

  // …
}

// …

async function closeTransport(transport) {
  // Respond to connection closing
  try {
    await transport.closed;
    console.log(`The HTTP/3 connection to ${url} closed gracefully.`);
  } catch (error) {
    console.error(`The HTTP/3 connection to ${url} closed due to ${error}.`);
  }
}