Page-specific js

application_controller.rb

class ApplicationController < ActionController::Base
  protected
  def update_page(callback_base_name = @action_name, &block)
    callback_name = "on_#{callback_base_name}"
    render :update do |page|
      args = block ? instance_eval(&block) : []
      args = [args] unless args.is_a?(Array)
      page << "page.#{callback_name}.apply(page, #{args.to_json})"
    end
  end
end

application_helper.rb

module ApplicationHelper
  def init_specific_javascript
    javascript_tag("Pages.activatePage('#{@controller.controller_path.camelcase}', '#{@controller.action_name}')")
  end
end

page.js

var Pages = new Object();
Pages.all = {};

Pages.add = function(name, methods) {
  var page = new Pages.Page(name);
  $.extend(page, methods);
  return page;
}

var page;
Pages.activatePage = function(controllerName, actionName) {
  page = Pages.all[controllerName];
  if(page) {
    $(document).ready(function() {
      if(page.all) page.all();
      if(page[actionName]) page[actionName].call(page);
    });
  }
}

Pages.Page = function(name) {
  this.name = name;
  Pages.all[name] = this;
}

users.js

Pages.add("Users", {
  all: function() {
    // Run this onload for all pages in the UsersController
  },
  show: function() {
    // Run this onload for the UsersController#show action
  },
  on_show: function() {
    // The UsersController#show xhr response runs this
  }
});

users_controller.rb

class UsersController < ActionController::Base
  def show
    @user = User.find(params[:id])
    respond_to do |format|
      format.html
      format.js do
        update_page { render(:partial => 'users/show') }
      end
    end
  end
end