PerformanceResourceTiming: nextHopProtocol property

The nextHopProtocol property can have the following values:

• A string representing the network protocol used to fetch the resource, as identified by the ALPN Protocol ID (RFC7301). Typical values are:
  • "http/0.9"
  • "http/1.0"
  • "http/1.1"
  • "h2"
  • "h2c"
  • "h3"
• An empty string if the resource is a cross-origin request and no Timing-Allow-Origin HTTP response header is used.

The nextHopProtocol property can be used to see resources that don't use the HTTP/2 or HTTP/3 protocols.

Example using a PerformanceObserver, which notifies of new resource performance entries as they are recorded in the browser's performance timeline. Use the buffered option to access entries from before the observer creation.

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    const protocol = entry.nextHopProtocol;
    if (protocol && !(protocol === "h2" || protocol === "h3")) {
      console.log(`${entry.name} uses ${protocol}.`);
    }
  });
});

observer.observe({ type: "resource", buffered: true });

Example using Performance.getEntriesByType(), which only shows resource performance entries present in the browser's performance timeline at the time you call this method:

const resources = performance.getEntriesByType("resource");
resources.forEach((entry) => {
  const protocol = entry.nextHopProtocol;
  if (protocol && !(protocol === "h2" || protocol === "h3")) {
    console.log(`${entry.name} uses ${protocol}.`);
  }
});

If the value of the nextHopProtocol property is an empty string, the resource might be a cross-origin request. To expose cross-origin network protocol information, the Timing-Allow-Origin HTTP response header needs to be set.

For example, to allow https://developer.mozilla.org to see network protocol information, the cross-origin resource should send:

Timing-Allow-Origin: https://developer.mozilla.org

• Timing-Allow-Origin
• HTTP/2
• HTTP/3