Events and propagation

Key points

1. 1A click travels in three phases: capture from window down to the target, the target itself, then bubbling back up to window.
2. 2Listeners run in the bubbling phase by default. Pass true or { capture: true } as the third argument to run in the capture phase.
3. 3stopPropagation stops the event from travelling further along its path, so elements after this one never get it. preventDefault cancels the browser's default action, such as following a link or submitting a form.
4. 4removeEventListener needs the same function reference and capture flag. An AbortController signal removes many listeners with one abort call.
5. 5new CustomEvent(type, { detail, bubbles }) carries data; dispatchEvent runs the listeners synchronously and returns false if a listener cancelled a cancelable event.