Add requireNamespace so str_view() fails more gracefully (#273)

Fixes #263

Author: AmeliaMN

R/view.R

@@ -75,6 +75,10 @@ str_view_widget <- function(lines) {
   )
   html <- htmltools::HTML(bullets)
 
+  if (!requireNamespace("htmlwidgets", quietly = TRUE)) {
+    stop("htmlwidgets package required for str_view(). \nPlease install.packages(\"htmlwidgets\") to use this functionality.",
+         call. = FALSE)
+  }
   size <- htmlwidgets::sizingPolicy(
     knitr.figure = FALSE,
     defaultHeight = pmin(10 * length(lines), 300),