Time To First Byte

// Measure the time to first byte of all the resources loaded
// https://webperf-snippets.nucliweb.net
new PerformanceObserver((entryList) => {
  const [pageNav] = entryList.getEntriesByType("navigation");
  console.log(`TTFB (ms): ${pageNav.responseStart}`);
}).observe({
  type: "navigation",
  buffered: true,
});

// Measure the time to first byte of all the resources loaded
// https://webperf-snippets.nucliweb.net
new PerformanceObserver((entryList) => {
  const entries = entryList.getEntries();
  const resourcesLoaded = [...entries].map((entry) => {
    let obj = {};
    // Some resources may have a responseStart value of 0, due
    // to the resource being cached, or a cross-origin resource
    // being served without a Timing-Allow-Origin header set.
    
    if (entry.responseStart > 0) {
      obj = {
        "TTFB (ms)": +entry.responseStart.toFixed(2),
        Resource: entry.name,
      };
    }
    return Object.keys(obj).length > 0 ? obj : undefined;
  })
  .filter((item) => item !== undefined);
 
  console.table(resourcesLoaded);
}).observe({
  type: "resource",
  buffered: true,
});