According to this blog post Active Admin monthly downloads nearly doubled last year to almost 3,000 times a day.  Part of that can probably be attributed to increasing use of continuous integration, but more interesting is that Active Admin has outpaced the competition. Possible contributing factors include three releases, including a 1.0 release that coincided with RailsConf and was featured by Ruby Weekly, a GoRails episode by Chris Oliver at the end of 2016, and the blog post by Charlie Gleason on using Active Admin as a back end to a React application, that has been discovered and tweeted by new fans repeatedly. I’ld love to think that timely responses to GitHub issues and pull requests and StackOverflow answers have helped also, along with the curated wiki and continuing contributions by plugin authors. Also there have been Japanese blog posts and activity so more adoption there. At this point Active Admin has 7,800 GitHub stars and 2.9M downloads, it will interesting to see how things are another year from now.

Arbre is a component based server side DOM rendering library written in Ruby.  Arbre was extracted from Active Admin from 2011-2012  but has not gained widespread use elsewhere.  As of September 2017 there were around 4M downloads to date from RubyGems and barely 450 stars on GitHub.

class Panel < Arbre::Component
  builder_method :panel

  def build(title, attributes = {})
    super(attributes)

    h3(title, class: "panel-title")
  end
end

React is a component based isomorphic DOM rendering library written in Javascript.  npm downloads have reached 40M in the past couple of years and the project has 75,000 stars on GitHub: it’s no contest really.  If you prefer Ruby over ES6 an Opal wrapper is available as hyper-react .

class App < Hyperloop::Component
  render(DIV) do 
    MainNavigation {} 
    PageContents {} 
    Footer {} 
  end
end

The APIs for both are relatively simple.

Arbre has builder_method to register components.  Each component has a build method which adds tags to an Arbre::Context that is eventually output using to_s.

React components have a render method that adds elements to a virtual DOM that is synchronized with the browser DOM as needed.

The most obvious difference is that Arbre does not integrate Javascript event handlers: it uses an unobtrusive approach that leaves registering event handlers to accompanying ES6/Coffeescript/Opal files.

Being exclusively server-side means that Arbre can and has been used with ActionView helpers and templates.  There are bugs but it mostly works.  Arbre is relatively simple and provides what Active Admin needs without further dependencies.

React components are careful about maintaining state and re-render when state is changed.  Arbre components get re-instantiated for each request and are more ad hoc.

Is anything to be learned from this comparison?  The prospects of widespread adoption of Arbre are slim to none.  An increasing number of developers are going to be looking to use a Rails admin framework with React, and that is where opportunity lies.