The Event Timing API is part of the Performance Timeline and is used to measure the performance of user interactions. Certain Events will have an interactionId value assigned to them, and this is useful for grouping related interactions based on common physical user inputs or gestures. This feature adds a very trivial performance.interactionCount, which is just the total number of interactions that have occured on the page. In particular, this feature is useful for computing the Interaction to Next Paint (INP) metric value, which requires knowing the total number of interactions in order to compute a high percentile score (p98 for pages with greater than 50 total interactions). This feature has been specced for a long while, was prototypes in Chromium a long time ago but never shipped, is part of Interop 2025, and is already available in other browsers. (Note: there is already a more powerful performance.eventCounts map for specific events, but it is not possible to accurately map event counts to interaction counts.)
Used to count the number of important real user interactions with a page. This is distinct from counting the number of events that Event Timing measures (because a single physical user gesture may fire many, variable number, of specific events, depending on the type of input and event target and page design) but you can already count interactions (inconveniently) by just counting the number of unique interactionId values in Event Timing API. Used for calculating Interaction to Next Paint (INP) metric.
Docs: https://www.w3.org/TR/event-timing/#dom-performance-interactioncount https://www.w3.org/TR/event-timing/#sec-increasing-interaction-count
Samples: https://chrome.dev/inp-demo