The parameter passed into the oninstall handler, the InstallEvent interface represents an install action that is dispatched on the ServiceWorkerGlobalScope of a ServiceWorker. As a child of ExtendableEvent, it ensures that functional events such as FetchEvent are not dispatched during installation. 

API InstallEvent Interface offline Offline Reference Service Workers ServiceWorker Workers

The activeWorker read-only property of the InstallEvent interface returns the ServiceWorker that is currently actively controlling the page.

activeWorker API InstallEvent Property Reference Service Workers ServiceWorker

The InstallEvent() constructor creates a new InstallEvent object.

API Constructor Experimental Expérimental InstallEvent Reference Service Workers ServiceWorker