gauge_size: Gauge size
In JohnCoene/g2r: Grammar of Graphics for Interactive Visualisations

Gauge size given a range or a JavaScript callback function.

1	gauge_size(g2, range = NULL, callback = NULL)

`g2`	An object of class `g2r` as returned by `g2r`.
`range`	A vector indicating the minimum and maximum sizes.
`callback`	A JavaScript callback function (see `cb`) which returns a color.

func <- cb("function(dist){
  if(dist > 60)
    return 20
  return 5
}")

g2(cars, asp(speed, dist, size = dist)) %>% 
  fig_point() %>% 
  gauge_size(callback = func)