diff --git a/experiments/carousel.html b/experiments/carousel.html
new file mode 100644
index 0000000..979dd38
--- /dev/null
+++ b/experiments/carousel.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+
+<html>
+<head>
+  <title>Carousel app</title>
+</head>
+
+<body id="body">
+
+<div id="ROOT" />
+
+<script type="text/javascript" src="nimcache/carousel.js"></script>
+
+</body>
+</html>
diff --git a/experiments/example.nim b/experiments/carousel.nim
similarity index 89%
rename from experiments/example.nim
rename to experiments/carousel.nim
index fa1e739..a820be7 100644
--- a/experiments/example.nim
+++ b/experiments/carousel.nim
@@ -1,3 +1,4 @@
+## This demo shows how you can develop your own stateful components with Karax.
 
 import vdom, vstyles, karax, karaxdsl, jdict, jstrutils, kdom
 
@@ -7,7 +8,6 @@ type
     cntdown, myid: int
     timer: TimeOut
     list: seq[cstring]
-    change: bool
 
 const ticksUntilChange = 5
 
@@ -24,11 +24,10 @@ proc render(x: VComponent): VNode =
       self.cntdown = ticksUntilChange
     else:
       self.timer = setTimeout(docount, 30)
-    self.change = true
+    markDirty(self)
     redraw()
 
   proc onclick(ev: Event; n: VNode) =
-    self.change = false
     if self.timer != nil:
       clearTimeout(self.timer)
     self.timer = setTimeout(docount, 30)
@@ -51,12 +50,8 @@ proc render(x: VComponent): VNode =
 
 var gid: int
 
-proc changed(c: VComponent): bool =
-  let x = Carousel(c)
-  result = x.change
-
 proc carousel(): Carousel =
-  result = newComponent(Carousel, render, changed)
+  result = newComponent(Carousel, render)
   result.list = images
   result.cntdown = ticksUntilChange
   result.myid = gid
diff --git a/experiments/example.nims b/experiments/carousel.nims
similarity index 100%
rename from experiments/example.nims
rename to experiments/carousel.nims
diff --git a/experiments/example.html b/experiments/example.html
deleted file mode 100644
index 2303d95..0000000
--- a/experiments/example.html
+++ /dev/null
@@ -1,15 +0,0 @@
-<!DOCTYPE html>
-
-<html>
-<head>
-  <title>Todo app</title>
-</head>
-
-<body id="body">
-
-<div id="ROOT" />
-
-<script type="text/javascript" src="nimcache/example.js"></script>
-
-</body>
-</html>
diff --git a/src/karax.nim b/src/karax.nim
index 42be93f..57c5162 100644
--- a/src/karax.nim
+++ b/src/karax.nim
@@ -225,6 +225,7 @@ proc updateElement(parent, current: Node, newNode, oldNode: VNode;
       assert oldNode.kind == VNodeKind.component
       let x = VComponent(oldNode)
       n = vnodeToDom(x.renderImpl(x), kxi)
+      x.updatedImpl(x)
       result = true
     else:
       detach(oldNode)
diff --git a/src/vdom.nim b/src/vdom.nim
index 8c19ea2..4edcd4e 100644
--- a/src/vdom.nim
+++ b/src/vdom.nim
@@ -119,11 +119,16 @@ type
     dom*: Node ## the attached real DOM node. Can be 'nil' if the virtual node
                ## is not part of the virtual DOM anymore.
 
-  VComponent* = ref object of VNode
+  VComponent* = ref object of VNode ## The abstract class for every karax component.
     renderImpl*: proc(self: VComponent): VNode
     changedImpl*: proc(self: VComponent): bool
+    updatedImpl*: proc(self: VComponent)
     onAttachImpl*: proc(self: VComponent)
     onDetachImpl*: proc(self: VComponent)
+    version*: int         ## Update this to trigger a redraw by karax. Usually you
+                          ## should call 'markDirty' instead which is an alias for
+                          ## 'inc version'.
+    renderedVersion*: int ## Do not touch. Used by karax.
 
 proc value*(n: VNode): cstring = n.text
 proc `value=`*(n: VNode; v: cstring) = n.text = v
@@ -143,15 +148,28 @@ proc vthunk*(name: cstring; args: varargs[VNode, vn]): VNode =
 proc dthunk*(name: cstring; args: varargs[VNode, vn]): VNode =
   VNode(kind: VNodeKind.dthunk, text: name, key: -1, kids: @args)
 
+proc defaultChangedImpl*(v: VComponent): bool =
+  ## The default implementation of 'changed'.
+  result = v.version != v.renderedVersion
+
+proc defaultUpdatedImpl*(v: VComponent) =
+  v.renderedVersion = v.version
+
 template newComponent*[T](t: typeDesc[T];
                  render: (proc(self: VComponent): VNode) not nil,
-                 changed: (proc(self: VComponent): bool) not nil,
                  onAttach: proc(self: VComponent) = nil,
-                 onDetach: proc(self: VComponent) = nil): T =
+                 onDetach: proc(self: VComponent) = nil,
+                 changed: (proc(self: VComponent): bool) = defaultChangedImpl,
+                 updated: proc(self: VComponent) = defaultUpdatedImpl): T =
   ## Use this template to create new components.
   T(kind: VNodeKind.component, key: -1,
     text: cstring(astToStr(t)), renderImpl: render,
-    changedImpl: changed, onAttachImpl: onAttach, onDetachImpl: onDetach)
+    changedImpl: changed, updatedImpl: updated,
+    onAttachImpl: onAttach, onDetachImpl: onDetach)
+
+template markDirty*(c: VComponent) =
+  ## mark the component as dirty so that it is re-rendered.
+  inc c.version
 
 proc setAttr*(n: VNode; key: cstring; val: cstring = "") =
   if n.attrs.isNil: