Extension points for plugins
dispatch(
  map,
  funcName,
  leaflet = stop(paste(funcName, "requires a map proxy object")),
  leaflet_proxy = stop(paste(funcName, "does not support map proxy objects"))
)invokeMethod(map, data, method, ...)
dispatch returns the value of leaflet or
leaflet_proxy, or an error. invokeMethod returns the
map object that was passed in, possibly modified.
a map object, as returned from leaflet or
leafletProxy
the name of the function that the user called that caused
this dispatch call; for error message purposes
an action to be performed if the map is from
leaflet
an action to be performed if the map is from
leafletProxy
a data object that will be used when evaluating formulas in
...
the name of the JavaScript method to invoke
unnamed arguments to be passed to the JavaScript method