Map two sf objects on one map with mapview

If you want to style both of them can do

mapview(elemZones, ...) +
  mapview(precincts, ...)

where the ... here refer to additional styling.

If you only want to style one of them you can simply do

mapview(elemZones) +
  precincts

mapview used to have a function addFeature() that is now in leafem

m <- mapview(elemZones, ...)
leafem::addFeatures(m, precincts)