Returns the time at which event dispatch started.


Returns the time at which the event dispatch ended.


Returns the associated event's cancelable attribute.

Returns the associated event's last target, if it is not removed.



Converts the PerformanceEventTiming object to JSON.


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. The first input delay or FID, measures the time from when a user first interacts with a page (i.e. when they click a link or tap on a button) to the time when the browser is actually able to begin processing event handlers in response to that interaction.

// Keep track of whether (and when) the page was first hidden, see:
// 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.
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.

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

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


Event Timing API
# sec-performance-event-timing

Browser compatibility

BCD tables only load in the browser