The addEventListener() method of the EventTarget interface sets up a function that will be called whenever the specified event is delivered to the target.
Optionaloptions: boolean | AddEventListenerOptionsOptionaloptions: boolean | AddEventListenerOptionsThe dispatchEvent() method of the EventTarget sends an Event to the object, (synchronously) invoking the affected event listeners in the appropriate order.
The removeEventListener() method of the EventTarget interface removes an event listener previously registered with EventTarget.addEventListener() from the target.
Optionaloptions: boolean | EventListenerOptionsOptionaloptions: boolean | EventListenerOptions
One opening of the viewer, for the page that asked for it.
It tells of the files shown and of editing until another opening takes over, and of the viewer closing in any case: a page passing its file on to another with
open()still hears the viewer close.