diff --git a/r/pkgdown/extra.js b/r/pkgdown/extra.js
index d9e3b32ee9d06..ec7a9b2a9f75f 100644
--- a/r/pkgdown/extra.js
+++ b/r/pkgdown/extra.js
@@ -17,6 +17,12 @@
 
 function check_page_exists_and_redirect(event) {
 
+    /**
+       * When a user uses the version dropdown in the docs, check if the page
+       * they are currently browsing exists in that version of the docs.
+       * If yes, take them there; if no, take them to the main docs page.
+       */
+
     const path_to_try = event.target.value;
 
     const base_path = path_to_try.match("(.*\/r\/)?")[0];
@@ -95,32 +101,48 @@ $(window).bind("pageshow", function(event) {
        * dropdown where you can select the version of the docs to view.
        */
 
+         // Get the start of the path which includes the version number or "dev"
+         // where applicable and add the "/docs/" suffix
         $pathStart = function(){
     	  return window.location.origin + "/docs/";
         }
 
+
+        // Get the end of the path after the version number or "dev" if present
         $pathEnd  = function(){
       	  var current_path = window.location.pathname;
-      	  return current_path.match("(?<=\/r).*");
+      	  // Can't do this via a positive look-behind or we lose Safari compatibility
+      	  return current_path.match("\/r.*")[0].substr(2);
         }
 
+        // Load JSON file mapping between docs version and R package version
         $.getJSON("https://arrow.apache.org/docs/r/versions.json", function( data ) {
           // get the current page's version number:
-		  var displayed_version = $('.version').text();
+    		  var displayed_version = $('.version').text();
+    		  // Create a dropdown selector and add the appropriate attributes
           const sel = document.createElement("select");
           sel.name = "version-selector";
           sel.id = "version-selector";
           sel.classList.add("navbar-default");
+          // When the selected value is changed, take the user to the version
+          // of the page they are browsing in the selected version
           sel.onchange = check_page_exists_and_redirect;
 
-		  $.each( data, function( key, val ) {
+          // For each of the items in the JSON object (name/version pairs)
+    		  $.each( data, function( key, val ) {
+    		    // Add a new option to the dropdown selector
             const opt = document.createElement("option");
+            // Set the path based on the 'version' field
             opt.value = $pathStart() + val.version + "r" + $pathEnd();
+            // Set the currently selected item based on the major and minor version numbers
             opt.selected = val.name.match("[0-9.]*")[0] === displayed_version;
+            // Set the displayed text based on the 'name' field
             opt.text = val.name;
+            // Add to the selector
             sel.append(opt);
-		  });
+  		    });
 
+          // Replace the HTML "version" component with the new selector
           $("span.version").replaceWith(sel);
         });
     });