reactiveLayer.R

library(leaflet)

map = leaflet() %>%
    addTiles() 

m = htmlwidgets::onRender(
    map,
    jsCode = htmlwidgets::JS(
        "function(el,x,data){
          var map = this;
          var tst = L.circleMarker([30, 30]);
          
          L.polyline([[0, -180],[0, 180]], {
            //'dashArray': [10, 50]
          })
          .on('click', function (e) {
              if (!map.hasLayer(tst)) {
                map.addLayer(tst);
              }
              console.log(map.hasLayer(tst));
          
              e.target.setStyle({
                color: 'red'
              });
          })
          .on('contextmenu', function (e) {
              e.target.setStyle({
                color: 'blue'
              });
              if (map.hasLayer(tst)) {
                map.removeLayer(tst);
              }
              console.log(map.hasLayer(tst));
          })
          .addTo(map);
        }
        "
    )
)

m

This is now available through leafem:::addReactiveFeatures()

library(leaflet)
library(leafem)
library(sf)
library(geojsonsf)

fran = mapview::franconia
brew = st_join(mapview::breweries, fran)

leaflet() %>%
  addTiles() %>%
  addGeoJSON(sf_geojson(fran), group = "fran") %>%
  leafem:::addReactiveFeatures(
    brew
    , bindTo = "fran"
    , by = "NUTS_ID"
    , on = "click"
    , group = "brew"
    , style = list(color = "black", fillOpacity = 0.9)
  ) %>%
  addMouseCoordinates() %>%
  setView(lng = 10.75, lat = 49.75, zoom = 8)