diff --git a/experiments/example.html b/experiments/example.html
index 35b9837..2303d95 100644
--- a/experiments/example.html
+++ b/experiments/example.html
@@ -3,7 +3,6 @@
 <html>
 <head>
   <title>Todo app</title>
-  <link rel="stylesheet" href="style.css">
 </head>
 
 <body id="body">
@@ -11,9 +10,6 @@
 <div id="ROOT" />
 
 <script type="text/javascript" src="nimcache/example.js"></script>
-<script type="text/javascript">
-  onload(window.location.pathname.split('/')[1])
-</script>
 
 </body>
 </html>
diff --git a/experiments/example.nim b/experiments/example.nim
index 0ea805e..3fe4000 100644
--- a/experiments/example.nim
+++ b/experiments/example.nim
@@ -1,135 +1,32 @@
 
-import vdom, karax, karaxdsl, jdict, jstrutils
-
-type
-  Filter = enum
-    all, active, completed
+import vdom, components, karax, karaxdsl, jdict, jstrutils
 
 var
-  entries: seq[(cstring, bool)]
-  selectedEntry = -1
-  filter: Filter
+  images: seq[cstring] = @[cstring"a", "b", "c", "d"]
 
-proc onTodoEnter(ev: Event; n: VNode) =
-  entries.add((n.value, false))
-  n.value = ""
+proc carousel*(key: VKey): VNode {.component.} =
+  state:
+    var counter: int = 0
 
-proc removeHandler(ev: Event; n: VNode) =
-  let id = suffixAsInt(n.id, "remove:")
-  entries[id] = (cstring(nil), false)
+  proc next(ev: Event; n: VNode) =
+    counter = (counter + 1) mod images.len
 
-proc editHandler(ev: Event; n: VNode) =
-  let id = suffixAsInt(n.id, "edit:")
-  selectedEntry = id
-
-when defined(usecache):
-  var entryCache = newJDict[int, VNode]()
-
-proc focusLost(ev: Event; n: VNode) = selectedEntry = -1
-
-proc editEntry(ev: Event; n: VNode) =
-  let id = suffixAsInt(n.id, "todo-edit:")
-  entries[id][0] = n.value
-  selectedEntry = -1
-
-proc toggleEntry(ev: Event; n: VNode) =
-  let id = suffixAsInt(n.id, "toggle:")
-  entries[id][1] = not entries[id][1]
-
-proc onAllDone(ev: Event; n: VNode) =
-  entries = @[]
-  selectedEntry = -1
-
-proc clearCompleted(ev: Event, n: VNode) =
-  for i in 0..<entries.len:
-    if entries[i][1]: entries[i][0] = nil
-
-proc toClass(completed: bool): cstring =
-  (if completed: cstring"completed" else: cstring"")
-
-proc toVis(visible: bool): cstring =
-  (if visible: cstring"visible" else: "hidden")
-
-proc toChecked(checked: bool): cstring =
-  (if checked: cstring"checked" else: cstring(nil))
-
-proc selected(v: Filter): cstring =
-  (if filter == v: cstring"selected" else: cstring(nil))
-
-proc createEntry(id: int; d: cstring; completed, selected: bool): VNode =
-  # implement caching:
-  when defined(usecache):
-    if entryCache.contains(i):
-      let old = entryCache[i]
-      return old
-
-  result = buildHtml(tr):
-    li(class=toClass(completed)):
-      if not selected:
-        tdiv(class = "view"):
-          input(class = "toggle", `type` = "checkbox", checked = toChecked(completed),
-                onclick=toggleEntry, id="toggle:" & &id)
-          label(onDblClick=editHandler, id="edit:" & &id):
-            text d
-          button(class = "destroy", id="remove:" & $id, onclick=removeHandler)
-      else:
-        input(class = "edit", name = "title", id = "todo-edit:" & &id,
-          onfocusLost = focusLost,
-          onenter = editEntry, value = d)
-  when defined(usecache):
-    entryCache[i] = result
+  result = buildHtml(tdiv(key=key)):
+    text images[counter]
+    button(onclick = next):
+      text "Next"
 
 proc createDom(): VNode =
-  result = buildHtml(tdiv(class="todomvc-wrapper")):
-    section(class = "todoapp"):
-      header(class = "header"):
-        h1:
-          text "todos"
-        input(class = "new-todo", placeholder="What needs to be done?", name = "newTodo",
-              onenter = onTodoEnter)
-      section(class = "main"):
-        input(class = "toggle-all", `type` = "checkbox", name = "toggle")
-        label(`for` = "toggle-all", onclick = onAllDone):
-          text "Mark all as complete"
-        var entriesCount = 0
-        var completedCount = 0
-        ul(class = "todo-list"):
-          for i, d in pairs(entries):
-            if d[0] != nil:
-              let b = case filter
-                      of all: true
-                      of active: not d[1]
-                      of completed: d[1]
-              if b:
-                createEntry(i, d[0], d[1], i == selectedEntry)
-              inc completedCount, ord(d[1])
-              inc entriesCount
-      footer(class = "footer"):
-        span(class = "todo-count"):
-          strong:
-            text(&entriesCount)
-          text cstring" item" & &(if entriesCount != 1: "s left" else: " left")
-        ul(class = "filters"):
-          li:
-            anchor(class = selected(all), href = "#/"):
-              text "All"
-          li:
-            anchor(class = selected(active), href = "#/active"):
-              text "Active"
-          li:
-            anchor(class = selected(completed), href = "#/completed"):
-              text "Completed"
-        button(class = "clear-completed", onclick = clearCompleted):
-          text "Clear completed (" & &completedCount & ")"
+  result = buildHtml(table):
+    tr:
+      td:
+        carousel(0)
+      td:
+        carousel(1)
+    tr:
+      td:
+        carousel(2)
+      td:
+        carousel(3)
 
-setOnHashChange(proc(hash: cstring) =
-  if hash == cstring"#/": filter = all
-  elif hash == cstring"#/completed": filter = completed
-  elif hash == cstring"#/active": filter = active
-)
 setRenderer createDom
-
-proc onload(session: cstring) {.exportc.} =
-  for i in 0..1: # 0_000:
-    entries.add((cstring"Entry " & &i, false))
-  init()
diff --git a/experiments/example.nims b/experiments/example.nims
new file mode 100644
index 0000000..6b5771c
--- /dev/null
+++ b/experiments/example.nims
@@ -0,0 +1 @@
+--path: "../src"
diff --git a/experiments/oldwidgets.nim b/experiments/oldwidgets.nim
index 023dc98..c947d7f 100644
--- a/experiments/oldwidgets.nim
+++ b/experiments/oldwidgets.nim
@@ -201,3 +201,51 @@ proc visibleKeys(e: Node; a, b: var VKey; h, count: var int) =
   else:
     for i in 0..<e.len:
       visibleKeys(e[i], a, b, h, count)
+
+template toState(x): untyped = "state" & x
+proc accessState(sv: string): NimNode {.compileTime.} =
+  newTree(nnkBracketExpr, newIdentNode(sv), newIdentNode("key"))
+
+proc stateDecl(n: NimNode; names: TableRef[string, bool]; decl, init: NimNode) =
+  case n.kind
+  of nnkVarSection, nnkLetSection:
+    for c in n:
+      expectKind c, nnkIdentDefs
+      let typ = c[^2]
+      let val = c[^1]
+      let usedType = if typ.kind != nnkEmpty: typ else: val
+      if usedType.kind == nnkEmpty:
+        error("cannot determine the variable's type", c)
+      for i in 0 .. c.len-3:
+        let v = $c[i]
+        let sv = toState v
+        decl.add quote do:
+          var `sv` = newJDict[VKey, `usedType`]()
+        if val.kind != nnkEmpty:
+          init.add newTree(nnkAsgn, accessState(sv), val)
+        names[v] = true
+  of nnkStmtList, nnkStmtListExpr:
+    for x in n: stateDecl(x, names, decl, init)
+  of nnkDo:
+    stateDecl(n.body, names, decl, init)
+  of nnkCommentStmt: discard
+  else:
+    error("invalid 'state' declaration", n)
+
+proc doState(n: NimNode; names: TableRef[string, bool];
+             decl, init: NimNode): NimNode =
+  result = n
+  case n.kind
+  of nnkCallKinds:
+    # handle 'state' declaration and remove it from the AST:
+    if n.len == 2 and repr(n[0]) == "state":
+      stateDecl(n[1], names, decl, init)
+      result = newTree(nnkEmpty)
+  of nnkSym, nnkIdent:
+    let v = $n
+    if v in names:
+      let sv = toState v
+      result = accessState(sv)
+  else:
+    for i in 0..<n.len:
+      result[i] = doState(n[i], names, decl, init)
diff --git a/src/components.nim b/src/components.nim
index fbbc00d..b93742d 100644
--- a/src/components.nim
+++ b/src/components.nim
@@ -2,6 +2,37 @@
 
 import macros, jdict, dom, vdom, tables, strutils
 
+type
+  StateDict*[V] = ref object
+    defaultValue*: V
+
+proc get[V](d: StateDict[V], k: VKey): V {.importcpp: "#[#]".}
+proc put[V](d: StateDict[V], k: VKey, v: V) {.importcpp: "#[#] = #".}
+
+proc contains*[V](d: StateDict[V], k: VKey): bool {.importcpp: "#.hasOwnProperty(#)".}
+proc del*[V](d: StateDict[V], k: VKey) {.importcpp: "delete #[#]".}
+
+proc newStateDict*[V](): StateDict[V] {.importcpp: "{@}".}
+
+var
+  dirty = newStateDict[bool]()
+  someDirty*: bool
+
+proc markDirty*(key: VKey) =
+  dirty.put(key, true)
+  someDirty = true
+
+proc unmarkDirty*(key: VKey) = dirty.del key
+proc isDirty*(key: VKey): bool = dirty.contains(key)
+
+proc `[]`*[V](d: StateDict[V], k: VKey): V =
+  if d.contains(k): result = d.get(k)
+  else: result = d.defaultValue
+
+proc `[]=`*[V](d: StateDict[V], k: VKey, v: V) =
+  d.put(k, v)
+  markDirty(k)
+
 var
   vcomponents* = newJDict[cstring, proc(args: seq[VNode]): VNode]()
   dcomponents* = newJDict[cstring, proc(args: seq[VNode]): Node]()
@@ -30,6 +61,63 @@ proc addTags() {.compileTime.} =
 static:
   addTags()
 
+
+template toState(x): untyped = newIdentNode("state" & x)
+proc accessState(sv: NimNode): NimNode {.compileTime.} =
+  newTree(nnkBracketExpr, sv, newIdentNode("key"))
+
+proc stateDecl(n: NimNode; names: TableRef[string, bool]; decl: NimNode) =
+  case n.kind
+  of nnkVarSection, nnkLetSection:
+    for c in n:
+      expectKind c, nnkIdentDefs
+      let typ = c[^2]
+      let val = c[^1]
+      let usedType = if typ.kind != nnkEmpty: typ else: newCall("type", val)
+      if usedType.kind == nnkEmpty:
+        error("cannot determine the variable's type", c)
+      for i in 0 .. c.len-3:
+        let v = $c[i]
+        let sv = toState v
+        decl.add quote do:
+          var `sv` = newStateDict[`usedType`]()
+        if val.kind != nnkEmpty:
+          decl.add newTree(nnkAsgn, newDotExpr(sv, newIdentNode"defaultValue"),
+                           val)
+        else:
+          error("component state must have a primitive initializer")
+        names[v] = true
+  of nnkStmtList, nnkStmtListExpr:
+    for x in n: stateDecl(x, names, decl)
+  of nnkDo:
+    stateDecl(n.body, names, decl)
+  of nnkCommentStmt: discard
+  else:
+    error("invalid 'state' declaration", n)
+
+proc doState(n: NimNode; names: TableRef[string, bool];
+             decl: NimNode): NimNode =
+  case n.kind
+  of nnkCallKinds:
+    # handle 'state' declaration and remove it from the AST:
+    if n.len == 2 and repr(n[0]) == "state":
+      stateDecl(n[1], names, decl)
+      return nil #newTree(nnkEmpty)
+  of nnkSym, nnkIdent:
+    let v = $n
+    if v in names:
+      let sv = toState v
+      return accessState(sv)
+  else: discard
+  result = copyNimNode(n)
+  for i in 0..<n.len:
+    let x = doState(n[i], names, decl)
+    if x != nil: result.add x
+
+proc compBody(body, decl: NimNode): NimNode =
+  var names = newTable[string, bool]()
+  result = doState(body, names, decl)
+
 proc unpack(symbolicType: NimNode; index: int): NimNode {.compileTime.} =
   #let t = symbolicType.getTypeImpl
   let t = repr(symbolicType)
@@ -67,7 +155,7 @@ macro component*(prc: untyped): untyped =
   for i in 0..6: n.add prc[i].copyNimTree
   expectKind(n, nnkProcDef)
   if n[0].kind == nnkEmpty:
-    error("please pass a non anonymous proc")
+    error("please pass a non anonymous proc", n[0])
   let name = n[0]
   let params = params(n)
   let rettype = repr params[0]
@@ -77,7 +165,7 @@ macro component*(prc: untyped): untyped =
   elif rettype == "Node":
     isvirtual = ComponentKind.Node
   else:
-    error "component must return VNode or Node"
+    error "component must return VNode or Node", params[0]
   let realName = if name.kind == nnkPostfix: name[1] else: name
   let nn = $realName
   n[0] = ident("inner" & nn)
@@ -91,6 +179,9 @@ macro component*(prc: untyped): untyped =
       unpackCall.add unpack(typ, counter)
       inc counter
 
+  let decl = newTree(nnkStmtList)
+  let newBody = compBody(n, decl)
+
   template vwrapper(pname, unpackCall) {.dirty.} =
     proc pname(args: seq[VNode]): VNode =
       unpackCall
@@ -107,7 +198,8 @@ macro component*(prc: untyped): untyped =
     bind jdict.`[]=`
     `[]=`(dcomponents, cstring(key), val)
 
-  result = newTree(nnkStmtList, n)
+  result = newTree(nnkStmtList, decl, newBody)
+
   if isvirtual == ComponentKind.VNode:
     result.add getAst(vwrapper(newname name, unpackCall))
     result.add getAst(vregister(newLit(nn), realName))
@@ -119,8 +211,15 @@ macro component*(prc: untyped): untyped =
     echo repr result
 
 when isMainModule:
-  proc public*(x, y: int, b: bool; s: cstring): VNode {.component.} =
-    discard
-  proc private(x, y: int, b: bool; s: cstring): VNode {.component.} =
-    discard
+  proc public*(key: VKey; x, y: int, b: bool; s: cstring): VNode {.component.} =
+    state:
+      var foo = 89
 
+    proc callback() =
+      foo = 78
+
+    let cc = callback
+
+  when false:
+    proc private(x, y: int, b: bool; s: cstring): VNode {.component.} =
+      discard
diff --git a/src/karax.nim b/src/karax.nim
index a535ae7..1908d6f 100644
--- a/src/karax.nim
+++ b/src/karax.nim
@@ -75,10 +75,12 @@ proc vnodeToDom(n: VNode): Node =
   elif n.kind == VNodeKind.vthunk:
     let x = callThunk(vcomponents[n.text], n)
     result = vnodeToDom(x)
+    n.key = result.key
     attach n
     return result
   elif n.kind == VNodeKind.dthunk:
     result = callThunk(dcomponents[n.text], n)
+    n.key = result.key
     attach n
     return result
   else:
@@ -145,7 +147,22 @@ proc equalsTree(a, b: VNode): bool =
       b.calcHash()
     return a.hash == b.hash
   else:
-    return eq(a, b)
+    result = eq(a, b)
+
+proc updateDirtyElements(parent, current: Node, newNode: VNode) =
+  if newNode.key >= 0 and isDirty(newNode.key):
+    unmarkDirty(newNode.key)
+    let n = vnodeToDom(newNode)
+    if parent == nil:
+      replaceById("ROOT", n)
+    else:
+      parent.replaceChild(n, current)
+  elif newNode.kind != VNodeKind.text and newNode.kind != VNodeKind.vthunk and
+       newNode.kind != VNodeKind.dthunk:
+    for i in 0..newNode.len-1:
+      updateDirtyElements(current, current[i], newNode[i])
+      # leave early if we know there cannot be anything left to do:
+      #if dirtyCount <= 0: return
 
 proc updateElement(parent, current: Node, newNode, oldNode: VNode) =
   if not equalsShallow(newNode, oldNode):
@@ -217,6 +234,9 @@ proc dodraw() =
     let olddom = document.getElementById("ROOT")
     updateElement(nil, olddom, newtree, currentTree)
     #assert same(newtree, document.getElementById("ROOT"))
+    if someDirty:
+      updateDirtyElements(nil, olddom, newtree)
+      someDirty = false
     currentTree = newtree
   # now that it's part of the DOM, give it the focus:
   if toFocus != nil:
diff --git a/src/vdom.nim b/src/vdom.nim
index d138c7a..25f6c12 100644
--- a/src/vdom.nim
+++ b/src/vdom.nim
@@ -124,10 +124,10 @@ template callThunk*(fn: typed; n: VNode): untyped =
   fn(n.kids)
 
 proc vthunk*(name: cstring; args: varargs[VNode, vn]): VNode =
-  VNode(kind: VNodeKind.vthunk, text: name, kids: @args)
+  VNode(kind: VNodeKind.vthunk, text: name, key: -1, kids: @args)
 
 proc dthunk*(name: cstring; args: varargs[VNode, vn]): VNode =
-  VNode(kind: VNodeKind.dthunk, text: name, kids: @args)
+  VNode(kind: VNodeKind.dthunk, text: name, key: -1, kids: @args)
 
 proc eq*(a, b: VNode): bool =
   if a.kind != b.kind: return false