@ch,
You can add easy buttons to add small JS events using addEasyButton() function.
Check out the below example -
leaflet() %>% addTiles() %>%
  addEasyButton(easyButton(
    icon="fa-globe", title="Zoom to Level 1",
    onClick=JS("function(btn, map){ map.setZoom(1); }"))) %>%
  addEasyButton(easyButton(
    icon="fa-crosshairs", title="Locate Me",
    onClick=JS("function(btn, map){ map.locate({setView: true}); }")))
Find more information about the example from the below link,
https://rstudio.github.io/leaflet/morefeatures.html