I have a shiny app with lots of points that need to be selected to display data in a table. I love the functionality displayed in this question here. Unfortunately implementing this in shiny produces the error message Ignoring prepended content; prependContent can't be used in a Shiny render call. My shiny app is rather large and requires internal data so I will post the example from the above linked question. If someone can get this working in shiny I can adapt it to my app.

library(leaflet)
library(crosstalk)
library(DT)
library(dplyr)
library(htmltools)
library(summarywidget)

data_2 <- data.frame(ID=c(1:8),
                     Name1 = c("A", "A", "A", "C", "B", "B", "A", "B"),
                     Name2 = c("a", "b", "b", "a", "b", "a", "b", "c"),
                     Value1 = c(12,43,54,34,23,77,44,22),
                     Value2 = c(6,5,2,7,5,6,4,3),
                     Lat = c(51.1, 51.6, 57.3, 52.4, 56.3, 54.3, 60.4, 49.2),
                     Lon = c(5, -3, -2, -1, 4, 3, -5, 0))

data_2<-data_2 %>%
  mutate(
    lab_DB = case_when(
      Name1 == unique(data_2$Name1)[1]  ~ "blue",
      Name1 == unique(data_2$Name1)[2]  ~ "green",
      Name1 == unique(data_2$Name1)[3]  ~  "red"
      
    )
  )


sdf <- SharedData$new(data_2, key=~ID, group="SharedDataqwertyui")


lmap <- leaflet() %>%
  addTiles() %>%
  addMarkers(data=sdf, group="test", layerId = ~ID) %>%
  htmlwidgets::prependContent(tags$script(src="https://unpkg.com/[email protected]/dist/leaflet-lasso.umd.min.js")) %>%
  htmlwidgets::onRender("
    function(el, x) {

      var sheet = window.document.styleSheets[0];
      sheet.insertRule('.selectedMarker { filter: hue-rotate(135deg); }', sheet.cssRules.length);

      var map = this;
      const lassoControl = L.control.lasso(options={'position':'topleft'}).addTo(map);

      function resetSelectedState() {
            map.eachLayer(layer => {
                if (layer instanceof L.Marker) {
                    layer.setIcon(new L.Icon.Default());
                } else if (layer instanceof L.Path) {
                    layer.setStyle({ color: '#3388ff' });
                }
            });
        }
        function setSelectedLayers(layers) {
            resetSelectedState();
            let ids = [];

            layers.forEach(layer => {
                if (layer instanceof L.Marker) {
                  layer.setIcon(new L.Icon.Default({ className: 'selected selectedMarker'}));
                } else if (layer instanceof L.Path) {
                    layer.setStyle({ color: '#ff4620' });
                }

                ids.push(layer.options.layerId);



            });
            ct_filter.set(ids);
        }


        var ct_filter = new crosstalk.FilterHandle('SharedDataqwertyui');
        ct_filter.setGroup('SharedDataqwertyui');

        var ct_sel = new crosstalk.SelectionHandle('SharedDataqwertyui');
        ct_sel.setGroup('SharedDataqwertyui');


        map.on('mousedown', () => {
            ct_filter.clear();
            ct_sel.clear();
            resetSelectedState();
        });
        map.on('lasso.finished', event => {
            setSelectedLayers(event.layers);
        });

        lassoControl.setOptions({ intersect: true});

        var clearSel = function(){
            ct_filter.clear();
            ct_sel.clear();
            resetSelectedState();
        }

        document.getElementById('clearbutton').onclick = clearSel;
    }") %>%
  addEasyButton(
    easyButton(
      icon = "fa-ban",
      title = "Clear Selection",
      id="clearbutton",
      onClick = JS("function(btn, map){
              return
         }")
    )
  ) 


dtable <- datatable(sdf , width = "100%",editable=TRUE, caption=tags$caption("Mean of Value1: ",summarywidget(sdf, statistic='mean', column='Value1')))

bscols( widths=c(6,6,0), lmap, dtable, htmltools::p(summarywidget(sdf, statistic='mean', column='Value1'), style="display:none;"))