Event

A signal that something happened in the browser — a click, a key press, or a page load — like a doorbell that tells your code someone's there.

An object dispatched through the DOM when user interaction or system activity occurs. Events propagate in three phases — capture, target, and bubble — and handlers registered via addEventListener respond to them.

The DOM Events spec defines an EventTarget dispatch algorithm that walks the composed path (accounting for shadow DOM boundaries) in capture then bubble order. Events implement the Event interface or subclasses (MouseEvent, KeyboardEvent, InputEvent). Passive listeners (passive: true) hint to the compositor that preventDefault() will not be called, enabling scroll optimization.