onRender: Execute custom JavaScript code after rendering

Description

Use this function to supplement the widget's built-in JavaScript rendering logic with additional custom JavaScript code, just for this specific widget object.

Usage

onRender(x, jsCode, data = NULL)

Arguments

An HTML Widget object

jsCode

Character vector containing JavaScript code (see Details)

data

An additional argument to pass to the jsCode function. This can be any R object that can be serialized to JSON. If you have multiple objects to pass to the function, use a named list.

Value

The modified widget object

Details

The jsCode parameter must contain valid JavaScript code which when evaluated returns a function.

The function will be invoked with three arguments: the first is the widget's main HTML element, and the second is the data to be rendered (the x parameter in createWidget). The third argument is the JavaScript equivalent of the R object passed into onRender as the data argument; this is an easy way to transfer e.g. data frames without having to manually do the JSON encoding.

When the function is invoked, the this keyword will refer to the widget instance object.

Examples

Run this code

# NOT RUN {
library(leaflet)

# This example uses browser geolocation. RStudio users:
# this won't work in the Viewer pane; try popping it
# out into your system web browser.
leaflet() %>% addTiles() %>%
  onRender("
    function(el, x) {
      // Navigate the map to the user's location
      this.locate({setView: true});
    }
  ")


# This example shows how you can make an R data frame available
# to your JavaScript code.

meh <- "😐";
yikes <- "😨";

df <- data.frame(
  lng = quakes$long,
  lat = quakes$lat,
  html = ifelse(quakes$mag < 5.5, meh, yikes),
  stringsAsFactors = FALSE
)

leaflet() %>% addTiles() %>%
  fitBounds(min(df$lng), min(df$lat), max(df$lng), max(df$lat)) %>%
  onRender("
    function(el, x, data) {
      for (var i = 0; i < data.lng.length; i++) {
        var icon = L.divIcon({className: '', html: data.html[i]});
        L.marker([data.lat[i], data.lng[i]], {icon: icon}).addTo(this);
      }
    }
  ", data = df)
# }
# NOT RUN {
# }