The read-only interactionId property returns an ID that uniquely identifies a user interaction which triggered a series of associated events.

When a user interacts with a web page, a user interaction (for example a click) usually triggers a sequence of events, such as pointerdown, pointerup, and click events. To measure the latency of this series of events, the events share the same interactionId.

An interactionId is only computed for the following event types belonging to a user interaction. It is 0 otherwise.

A number.

The following example collects event duration for all events corresponding to an interaction. The eventLatencies map can then be used to find events with maximum duration for a user interaction, for example.

// The key is the interaction ID.
let eventLatencies = {};

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    if (entry.interactionId > 0) {
      const interactionId = entry.interactionId;
      if (!eventLatencies.has(interactionId)) {
        eventLatencies[interactionId] = [];
      }
      eventLatencies[interactionId].push(entry.duration);
    }
  });
});

observer.observe({ type: "event", buffered: true });

// Log events with maximum event duration for a user interaction
Object.entries(eventLatencies).forEach(([k, v]) => {
  console.log(Math.max(...v));
});