TinyMCE, ActiveAdmin, and Rails 4

I was installing TinyMCE so I could have a WYSIWYG editor on a textarea within ActiveAdmin when I got the following error.

No route matches [GET] "/assets/tinymce/themes/advanced/theme.js"

I found the similar issue on the tinymce-rails gem’s docs. Losing TINY mce in dev when switching from 3.5.8 to 4.0.2 in Dev

The issue was caused by a change in TinyMCE’s theme. Apparently TinyMCE 4 replaced the ‘advanced’ theme with the ‘modern’ theme. Sure enough when I edited my active_admin.js.coffee CoffeeScript file to:

#= require active_admin/base
#= require tinymce
$(document).ready ->
  tinyMCE.init
    mode: "textareas"
    theme: "modern"
    editor_selector: "tinymce_editor"
  return

That solved the issue I was having. I followed along with this answer on StackOverflow to install tinyMCE to rails.