Make htmlwidgets work with knitr-powered Jekyll and GitHub Pages

knit_hook_setter.R

#' Set knitr hooks for htmlwidgets with Jekyll/GitHub Pages
#' 
#' This functions sets a `knitr` hook so that any HTML widgets that were
#'  printed (i.e., objects that inherit the `'htmlwidget'`, like those from 
#'  the `htmlwidgets` or `plotly` packages) will work with a Jekyll system, 
#'  like the one used for GitHub Pages. 
#' 
#' It essentially sets a hook so that, when the document is finished being
#'  knitted, it moves all the dependencies necessary for the widgets to a 
#'  directory, and then adds HTML code to the document to load those files 
#'  from their new location. Additionally, it sets the default 
#'  `screenshot.force` chunk option to `FALSE`, so `knitr` doesn't try to 
#'  use a screenshot instead of the widget.
#'  
#' See https://www.zachburchill.ml/plotly_with_jekyll/ for background 
#'  and (https://gist.github.com/burchill/9df0f6245ea7768e5b6bbd0a1c22db08) 
#'  for the old, bad version of this script.
#' 
#' @param dep_dir The directory you want to save the dependencies to.
#' @param base_path The directory you want to make the dependency links relative to. 
#'  For example, if your post is at the url `yoursite.com/this_post/`, then you'll 
#'  want to make `base_path` the home directory of your project.
#' @param hrefFilter This function lets you perform any additional manipulations 
#'  to the dependency links. For some reason, when I give my base directory as my
#'  project's home directory, the links come back without the necessary "/" in front 
#'  of them. This function adds that to each link.
#' @export
set_widget_hooks <- function(dep_dir, base_path, 
                             hrefFilter = function(x) paste0("/", x)) {
  
  # Move the dependencies into the specified folder,
  #  makes them relative to the base directory,
  #  and outputs the HTML that loads them.
  render_deps <- function() {
    l <- knitr::knit_meta(class = "html_dependency",
                          clean = FALSE)
    if (length(l) > 0)
      dir.create(dep_dir, showWarnings = FALSE, recursive = TRUE)
    l <- lapply(unique(l), function(dep) {
      dep <- htmltools::copyDependencyToDir(dep, dep_dir, FALSE)
      dep <- htmltools::makeDependencyRelative(dep, base_path, FALSE)
      dep } )
    l <- htmltools::renderDependencies(l,  hrefFilter=hrefFilter)
    htmltools::htmlPreserve(l)
  }
  
  # Adds the dependency-loading HTML at the end of the doc,
  #  without upsetting the previous doc-hook.
  prev_doc_hook <- knitr::knit_hooks$get("document")
  knitr::knit_hooks$set(document = function(x) {
    prev_doc_hook(append(x, render_deps()))
  })
  
  # Sets the default of all chunks to not force
  #  screenshots. You can change it to `TRUE`
  #  on the chunks you want it to screenshot.
  knitr::opts_chunk$set(screenshot.force=FALSE)
}