Is "knitr" required for certain outputs in R?

Question

I am trying to follow this post on stackoverflow (R Leaflet: Add a Range Slider to Filter Markers without Shiny). I copy and pasted the code below:

library( crosstalk )
library( leaflet )
library( dplyr )

data <- data.frame(id = c(1,2,3,4,5),
                   lat= c(50.9, 50.8, 50.5, 50.5, 51),
                   lon = c(-0.7, -0.92, -1, -0.8, -0.9),
                   date = c("2020-06-01", "2020-05-07", "2020-03-24", "2020-04-01", "2020-05-26"))

data <- data %>% dplyr::mutate( date2 = as.numeric( as.Date( date ) ),
                                date3 = as.Date( date )
                                )

shared_data <- SharedData$new( data )

filter_slider("date", "Date", shared_data, ~date3, width = "100%")
leaflet(shared_data, width = "100%", height = 800) %>%
  leaflet::addTiles() %>%
  leaflet::addMarkers() 

Yet when I run this code, the resulting map is missing the "slider":

• Does anyone know why this is happening? Is this because the "slider" requires the "knitr" package? Is it possible I might have to save this map as an "html" file for the slider to appear?

Thank you!

Answer 1

Yes, but in your case, the output discrepancy has nothing to do with knitr.

NOTE: the OP (appropriately) opened another question asking how to implement a slider and so this is brief since it is directly answering the question.