PerformanceResourceTiming.domainLookupStart

const dns = entry.domainLookupEnd - entry.domainLookupStart;

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    const dns = entry.domainLookupEnd - entry.domainLookupStart;
    if (dns > 0) {
      console.log(`${entry.name}: DNS lookup duration: ${dns}ms`);
    }
  });
});
observer.observe({ type: "resource", buffered: true });

const resources = performance.getEntriesByType("resource");
resources.forEach((entry) => {
  const dns = entry.domainLookupEnd - entry.domainLookupStart;
  if (dns > 0) {
    console.log(`${entry.name}: DNS lookup duration: ${dns}ms`);
  }
});

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