Custom-Metric.md

Custom Metric using Element Timing Origin Trial

bit.ly/element-timing-origin-trial

Time To First Cat(TTFC)

Calculate time to first cat(TTFC) HTML

<img src="best_cat.jpg" elementtiming>

JS

const observer = new PerformanceObserver(list => {
  list.getEntries().forEach(function(entry){
    const navStart = performance.timing.navigationstart;
    // ttfc = navigation until image rendered
    const ttfc = entry.startTime - navStart;
    console.log(`Time To First Cat ${ttfc}`)
  });
});
observer.observe({entryTypes: ['element']});