navigator.storage is no longer an EventTarget navigator.storage was made an EventTarget for the Storage Pressure Event, which never made it past the prototype phase: https://chromestatus.com/feature/5666274359115776 This dead code is being removed and as a result, navigator.storage will no longer extend EventTarget.
This web-visible change is a result of technical shortcomings that make it impossible to feature-gate changes to an API object's signature. In a world without that shortcoming, navigator.storage would have never been an EventTarget.