PerformanceEventTiming

The PerformanceEventTiming interface of the Event Timing API provides timing information for the event types listed below.

Properties

PerformanceEventTiming.processingStart: Returns the time at which event dispatch started.
PerformanceEventTiming.processingEnd: Returns the time at which the event dispatch ended.
PerformanceEventTiming.cancelable: Returns the associated event's cancelable attribute.
PerformanceEventTiming.target: Returns the associated event's last target, if it is not removed.

Methods

PerformanceEventTiming.toJSON(): Converts the PerformanceEventTiming object to JSON.

Examples

The following example shows how to use the API for all events:

const observer = new PerformanceObserver(function(list) {
    const perfEntries = list.getEntries().forEach(entry => {
        // Full duration
        const inputDuration = entry.duration;
        // Input delay (before processing event)
        const inputDelay = entry.processingStart - entry.startTime;
        // Synchronous event processing time (between start and end dispatch).
        const inputSyncProcessingTime = entry.processingEnd - entry.processingStart;
    });
});
// Register observer for event.
observer.observe({entryTypes: ["event"]});

We can also directly query the first input delay.

// Keep track of whether (and when) the page was first hidden, see:
// https://github.com/w3c/page-visibility/issues/29
// NOTE: ideally this check would be performed in the document <head>
// to avoid cases where the visibility state changes before this code runs.
let firstHiddenTime = document.visibilityState === 'hidden' ? 0 : Infinity;
document.addEventListener('visibilitychange', (event) => {
  firstHiddenTime = Math.min(firstHiddenTime, event.timeStamp);
}, {once: true});

// Sends the passed data to an analytics endpoint. This code
// uses `/analytics`; you can replace it with your own URL.
function sendToAnalytics(data) {
  const body = JSON.stringify(data);
  // Use `navigator.sendBeacon()` if available, falling back to `fetch()`.
  (navigator.sendBeacon && navigator.sendBeacon('/analytics', body)) ||
      fetch('/analytics', {body, method: 'POST', keepalive: true});
}

// Use a try/catch instead of feature detecting `first-input`
// support, since some browsers throw when using the new `type` option.
// https://bugs.webkit.org/show_bug.cgi?id=209216
try {
  function onFirstInputEntry(entry) {
    // Only report FID if the page wasn't hidden prior to
    // the entry being dispatched. This typically happens when a
    // page is loaded in a background tab.
    if (entry.startTime < firstHiddenTime) {
      const fid = entry.processingStart - entry.startTime;

      // Report the FID value to an analytics endpoint.
      sendToAnalytics({fid});
    }
  }

  // Create a PerformanceObserver that calls `onFirstInputEntry` for each entry.
  const po = new PerformanceObserver((entryList) => {
    entryList.getEntries().forEach(onFirstInputEntry);
  });

  // Observe entries of type `first-input`, including buffered entries,
  // i.e. entries that occurred before calling `observe()` below.
  po.observe({
    type: 'first-input',
    buffered: true,
  });
} catch (e) {
  // Do nothing if the browser doesn't support this API.
}

Specifications

Specification	Status	Comment
Unknown The definition of '[[Member]]' in that specification.	Unknown	Initial definition.

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`PerformanceEventTiming` Experimental	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`cancelable` Experimental	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`processingEnd` Experimental	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`processingStart` Experimental	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0
`toJSON` Experimental	Chrome Full support 77	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 77	Chrome Android Full support 77	Firefox Android No support No	Opera Android Full support Yes	Safari iOS No support No	Samsung Internet Android Full support 12.0

Legend

Full support: Full support
No support: No support
Experimental. Expect behavior to change in the future.: Experimental. Expect behavior to change in the future.