Performance Observer

Instead of polling the Peformance Timeline you can now (well, at least in Chrome Canary) subscribe to notifications of new performance metrics via Performance Observer! A simple example in action:

    var observer = new PerformanceObserver(function(list) {      
      list.getEntries().map(entry => {
        var pre = document.createElement('pre')
        pre.innerText = JSON.stringify(obj(entry), null, '\t');
    // Register for User and Resource Timing events
    observer.observe({entryTypes: ['resource', 'mark', 'measure']});
    // Log document state changes to performance timeline
    document.onreadystatechange = function () {

Observed performance metrics on this page...

    User Timing

    Defines the performance.mark and performance.measure methods that expose a high precision timestamp to developers so they can better measure the performance of their applications.

    Mark name:

    Measure name: Start mark (opt): End mark (opt):

    Resource Timing

    Observer receives notifications whenever a new Resource Timing event is registered with the performance timeline - i.e. whenever a resource fetch is finished...