more help from You

app/assets/javascript/opal_main.js.rb

@@ -6,17 +6,50 @@ require 'browser/setup/mini'
 class Kanta
   def initialize(hash)
     hash.each do |k,v|
-      instance_variable_set "@#{k}" , v
-      self.class.define_method k.to_sym do
-        instance_variable_get "@#{k}".to_sym
-      end
-      self.class.define_method "#{k}=".to_sym  do |new_v|
-        instance_variable_set "@#{k}" , new_v
-      end
+      wrap_attr(k,v)
     end
+    @effect = nil
+    @subscribers = {}
+  end
 
-    def mount(on_class)
-      puts $document[on_class].inner_html
+  def track( target , key )
+    return unless @effect
+    subs = get_subscribers_for(key)
+    subs << @effect
+  end
+
+  def trigger(key)
+    effects = get_subscribers_for(key)
+    effects.each {|effect| effect() }
+  end
+
+  def get_subscribers_for(key)
+    unless @subscribers.has_key?(key)
+      @subscribers[key] = []
+    end
+    @subscribers[key]
+  end
+
+  def mount(on_class)
+    puts $document[on_class].inner_html
+  end
+
+  def wrap_attr(k,v)
+    instance_variable_set "@#{k}" , v
+    define_getter(k)
+    define_setter(k)
+  end
+
+  def define_getter(k)
+    self.class.define_method k.to_sym do
+      track(key)
+      instance_variable_get "@#{k}".to_sym
+    end
+  end
+  def define_setter(k)
+    self.class.define_method "#{k}=".to_sym  do |new_v|
+      instance_variable_set "@#{k}" , new_v
+      trigger(key)
     end
   end
 end

app/views/kanta/show.html.haml

@@ -10,7 +10,7 @@
 
   end
 
-  kanta = Kanta.new(bg: 'bg-cyan-200')
+  kanta = Clicker.new(bg: 'bg-cyan-200')
   puts kanta.bg
   kanta.bg = "bg-cyan"
   puts kanta.bg