When you say object extent, what are you referring to exactly? Found this codepen Watching map view extents where you can add an output for view.zoom, change the initial extent to your values and then maybe get the zoom. ... But the Zoom levels (LOD) are predetermined by the map service, so that could be interesting.
Is this so you can zoom the map to a particular extent? If so, MapView.goTo() works with the Extent object.