WebTransport: responseHeaders property

Value

A Headers object, or null if the session has not yet been established.

The returned object is immutable: calling methods that modify it, such as set() or append(), throws a TypeError.

The session is set up using an extended CONNECT request. The client can add custom headers to this request using the headers constructor option. The server can include headers in its response to return application-specific information to the client, such as a session identifier.

The value is set before the ready promise fulfills.

The returned headers don't include WT-Protocol, which the server uses to indicate the application protocol it chose. Use WebTransport.protocol to get the selected protocol instead.

Examples

Reading response headers

This example shows how you might send a custom header when setting up a session and then read a header that the server returns in its response.

js

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

async function initTransport(url) {
  const transport = new WebTransport(url, {
    // Custom request headers
    headers: { Authorization: "Bearer abc123" },
  });

  // responseHeaders is null until the session is established
  console.log(transport.responseHeaders); // null

  await transport.ready;

  // Log all the response headers
  for (const [name, value] of transport.responseHeaders) {
    console.log(`${name}: ${value}`);
  }

  // Read a specific header
  const sessionId = transport.responseHeaders.get("X-Session-Id");
  console.log(`Session ID: ${sessionId}`);

  return transport;
}

initTransport(url);