Show Different Legend When Changing Layer - leaflet

I'm trying to make my leaflet map show no legend when both layers are selected, and when only one layer is selected show that layer's legend.

I found these solutions using Javascript:

• How to switch between multiple map legends with leaflet.js?
• https://gis.stackexchange.com/questions/92257/leaflet-add-and-remove-legends-with-layer-selection

But I haven't been able to figure out how to apply these techniques in R. Can anyone point me to a document to read, or could give me a hint?

Here is some test data:

df1
  Tickets      long      lat
1      28 -71.12088 42.37418
2       4 -71.09524 42.36911
3       3 -71.11935 42.38532
df2 
  Tickets     long      lat
4      33 -71.1213 42.37401
5       1 -71.0915 42.37255
6      21 -71.1226 42.37512
7       1 -71.1016 42.36411

Here is a snippet of code:

base_map <- leaflet() %>% 
  addProviderTiles('Stamen.TonerLite') %>% 
  setView(-71.128184, 42.3769824, zoom = 14)

pal1 <- colorNumeric(palette = "RdBu",
                    domain = df1$Tickets)
pal2 <- colorNumeric(palette = "RdBu",
                    domain = df2$Tickets)

base_map %>% 
    addCircles(data = df1, lng = df1$long, lat = df1$lat,
               color = pal1(df1$Tickets), radius = 5, group = "Group 1 Dots") %>%
    addLegend("bottomright", pal = pal1, values = df1$Tickets,
               title = "1 Dots") %>%
    addCircles(data = df2, lng = df2$long, lat = df2$lat,
               color = pal2(df2$Tickets), radius = 5, group = "Group 2 Dots") %>%
    addLegend("bottomright", pal = pal2, values = df2$Tickets,
               title = "2 Dots") %>%
    addLayersControl(overlayGroups = c("Group 1 Dots", "Group 2 Dots"),
                     options = layersControlOptions(collapsed = FALSE))

Thanks.