Example of User Timing API usage

fetch-some-data.js

const fetchSomeData = async () => {

  const measureName = 'fetchSomeData';
  const startMark = `[START]: ${measureName}`;
  const endMark = `[END]: ${measureName}`;

  try {
    const url = 'your-url';
    // starting the User Timing API marker for this request
    performance.mark(startMark);
    const data = await fetch(url);
    return data;
  } catch (error) {
    console.error('Oops!', error);
  } finally {
    // Finishing the markers and sending the results
    performance.mark(endMark);
    performance.measure(measureName, startMark, endMark);
    performance.clearMeasures(measureName);
    performance.clearMarks(startMark);
    performance.clearMarks(endMark);
  }
}