Preview a new layout with params

example.md

class PostsController < ApplicationController
  ...
  def show
    respond_to do |format|
      # If v2=enabled is in the URL (https://www.example.com/posts/1?v2=enabled) render the new layout.
      if params[:v2] == "enabled"
        format.html { render template: 'posts/show_v2' }
      # Otherwise load the existing layout.
      else
        format.html { render template: 'posts/show' }
      end
    end    
  end  
end