Make ObservableValue lazily calculate its value

react.rb

@@ -120,11 +120,15 @@ module React
       @valueProc = valueProc
       
       @dependencies = Hash.new
-      
-      update_value
+      @initialized = false
     end
 
     def value
+      if !@initialized
+        @initialized = true
+        update_value
+      end
+
       cur_ctx = React::Context.current!
       @dependencies[cur_ctx.id] = cur_ctx
       cur_ctx.on_invalidate do

server.rb

@@ -5,7 +5,7 @@ require 'digest/md5'
 shinyapp = ShinyApp.new
 
 input1 = React::ObservableValue.new {
-  (shinyapp.session.get('input1') || '') + (shinyapp.session.get('addnewline') ? "\n" : '')
+  shinyapp.session.get('input1') + (shinyapp.session.get('addnewline') ? "\n" : '')
 }
 
 shinyapp.define_output('md5_hash') do