Add option to open external links in new tab

_plugins/open_external_links_in_new_tab.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+require 'nokogiri'
+
+# If the configuration sets `open_external_links_in_new_tab` to a truthy value,
+# add 'target=_blank' to anchor tags that don't have `internal-link` class
+Jekyll::Hooks.register [:pages, :notes], :post_convert do |doc|
+  open_external_links_in_new_tab = !!doc.site.config["open_external_links_in_new_tab"]
+
+  if open_external_links_in_new_tab
+    parsed_doc = Nokogiri::HTML(doc.content)
+    parsed_doc.css("a:not(.internal-link)").each do |link|
+      link.set_attribute('target', 'blank')
+    end
+    doc.content = parsed_doc.to_html
+  end
+end