Is the Passive Attribute Important?

Passive passive means that you promise not to use the a cancel defaulta method on the event object. It's important because in some cases, if the system can assume that you cannot cancel the default behavior, it enables the browser to be much more efficient about doing certain things. In general, if you are not going to can do a inoeu, if ou put in an event handler and you know for a fact that you're not going to be cancelling the default action behaviour under any event, then it's better, from a performance point of view, to just put in the passive attribute.