An JavaScript illustrating the usage of the W3C Server Timing API

ServerTiming.js

if(!window.performance){
  document.writeln('<div class="alert alert-danger">Your browser does NOT the Performance API</div>');
} else {
  loopServerTiming: for (const entryType of ['navigation', 'resource']) {
    for (const {name: url, serverTiming} of performance.getEntriesByType(entryType)) {
      if(!serverTiming){
        document.writeln('<div class="alert alert-danger">Your browser does NOT the Server Timing API</div>');
        break loopServerTiming;
      }
      for (const {name, duration, description} of serverTiming) {
        document.writeln(
          '<div class="alert ' + (duration > 100 ? 'alert-danger' : 'alert-success')  + '" role="alert">' + 
          '<h5>' + description + ' <span class="badge badge-secondary">' + duration + 'ms.</span></h5>'+
          '<small>' + url + '</small>' + 
          '</div>'
        );
      }
    }
  }
}