The Leaflet JS mapping library has lots of plugins available. The Leaflet package for R provides direct support for some, but far from all, of these plugins, by providing R functions for invoking the plugins.
If you as an R user find yourself wanting to use a Leaflet plugin that isn't directly supported in the R package, you can use the technique shown here to load the plugin yourself and invoke it using JS code.
OK I'm sorry I didn't used the right keywords for my search, I felt on that: rstudio/shiny#1389
But I think I don't well understand the solution. I tried to install different versions of
htlmlwidgets
(included the development version) but it still doesn't work.