diff --git a/src/karax.nim b/src/karax.nim
index ed956d8..78395b3 100644
--- a/src/karax.nim
+++ b/src/karax.nim
@@ -135,6 +135,8 @@ proc equalsShallow(a, b: VNode): bool =
       if not equalsShallow(a[i], b[i]): return false
   if not sameAttrs(a, b): return false
   if a.class != b.class: return false
+  if a.track != 0 and b.track != 0:
+    if a.track != b.track: return false
   # XXX test event listeners here?
   return true
 
@@ -165,6 +167,7 @@ proc updateDirtyElements(parent, current: Node, newNode: VNode) =
       #if dirtyCount <= 0: return
 
 proc updateElement(parent, current: Node, newNode, oldNode: VNode) =
+  newNode.dom = oldNode.dom
   if not equalsShallow(newNode, oldNode):
     detach(oldNode)
     let n = vnodeToDom(newNode)
@@ -175,7 +178,6 @@ proc updateElement(parent, current: Node, newNode, oldNode: VNode) =
   elif newNode.kind != VNodeKind.text:
     let newLength = newNode.len
     var oldLength = oldNode.len
-    let minLength = min(newLength, oldLength)
     assert oldNode.kind == newNode.kind
     when defined(simpleDiff):
       for i in 0..min(newLength, oldLength)-1:
@@ -188,36 +190,46 @@ proc updateElement(parent, current: Node, newNode, oldNode: VNode) =
           detach(oldNode[i])
           current.removeChild(current.lastChild)
     else:
-      var commonPrefix = 0
-      while commonPrefix < minLength and
-          equalsTree(newNode[commonPrefix], oldNode[commonPrefix]):
-        inc commonPrefix
+        var left = 0
+        var rightNew = newLength - 1
+        var rightOld = oldLength - 1
 
-      var oldPos = oldLength - 1
-      var newPos = newLength - 1
-      while oldPos >= commonPrefix and newPos >= commonPrefix and
-          equalsTree(newNode[newPos], oldNode[oldPos]):
-        dec oldPos
-        dec newPos
+        while left <= min(rightNew, rightOld):
+          var minRight = min(rightOld, rightNew)
 
-      var pos = min(oldPos, newPos) + 1
-      for i in commonPrefix..pos-1:
-        updateElement(current, current.childNodes[i], newNode[i], oldNode[i])
+          while left <= minRight and
+              equalsTree(newNode[left], oldNode[left]):
+            newNode[left] = oldNode[left]
+            inc left
 
-      var nextChildPos = oldPos + 1
-      while pos <= newPos:
-        if nextChildPos == oldLength:
-          current.appendChild(vnodeToDom(newNode[pos]))
-        else:
-          current.insertBefore(vnodeToDom(newNode[pos]), current.childNodes[nextChildPos])
-        # added new Node, so old state of VDOM have one more Node
-        inc oldLength
-        inc pos
-        inc nextChildPos
+          while rightOld > left and rightNew > left and
+              equalsTree(newNode[rightNew], oldNode[rightOld]):
+            newNode[rightNew] = oldNode[rightOld]
+            dec rightOld
+            dec rightNew
 
-      for i in pos..oldPos:
-        detach(oldNode[i])
-        current.removeChild(current.childNodes[pos])
+          minRight = min(rightOld, rightNew)
+          if left <= minRight:
+            updateElement(current, oldNode[left].dom, newNode[left], oldNode[left])
+            inc left
+
+          if left < minRight:
+            updateElement(current, oldNode[rightOld].dom, newNode[rightNew], oldNode[rightOld])
+            dec rightNew
+            dec rightOld
+
+        var posNextElem = rightOld + 1
+        var isPushBack = posNextElem == oldLength
+        while left <= rightNew:
+          if isPushBack:
+            current.appendChild(vnodeToDom(newNode[left]))
+          else:
+            current.insertBefore(vnodeToDom(newNode[left]), oldNode[posNextElem].dom)
+          inc left
+
+        for i in left..rightOld:
+          current.removeChild(oldNode[i].dom)
+          detach(oldNode[i])
 
 when false:
   var drawTimeout: Timeout
@@ -256,6 +268,8 @@ proc redraw*() =
   else:
     dodraw()
 
+proc redrawForce*() = dodraw()
+
 proc init(ev: Event) =
   reqFrame(dodraw)
 
@@ -263,6 +277,12 @@ proc setRenderer*(renderer: proc (): VNode) =
   dorender = renderer
   window.onload = init
 
+proc setRendererOnly*(renderer: proc (): VNode) =
+  dorender = renderer
+
+proc setOnloadOnly*() =
+  window.onload = init
+
 proc addEventHandler*(n: VNode; k: EventKind; action: EventHandler) =
   ## Implements the foundation of Karax's event management.
   ## Karax DSL transforms ``tag(onEvent = handler)`` to
diff --git a/src/karaxdsl.nim b/src/karaxdsl.nim
index 5ba525a..5553d8f 100644
--- a/src/karaxdsl.nim
+++ b/src/karaxdsl.nim
@@ -4,7 +4,7 @@ from strutils import startsWith, toLowerAscii
 
 const
   StmtContext = ["kout", "inc", "echo", "dec", "!"]
-  SpecialAttrs = ["id", "class", "value", "key"]
+  SpecialAttrs = ["id", "class", "value", "key", "track"]
 
 proc getName(n: NimNode): string =
   case n.kind
diff --git a/src/vdom.nim b/src/vdom.nim
index 25f6c12..599ea08 100644
--- a/src/vdom.nim
+++ b/src/vdom.nim
@@ -106,8 +106,10 @@ type
     # even index: key, odd index: value; done this way for memory efficiency:
     attrs: seq[cstring]
     events*: seq[(EventKind, EventHandler)]
-    hash*: Hash
-    validHash*: bool
+    when false:
+      hash*: Hash
+      validHash*: bool
+    track*: int
     dom*: Node ## the attached real DOM node. Can be 'nil' if the virtual node
                ## is not part of the virtual DOM anymore.
 
@@ -130,6 +132,9 @@ proc dthunk*(name: cstring; args: varargs[VNode, vn]): VNode =
   VNode(kind: VNodeKind.dthunk, text: name, key: -1, kids: @args)
 
 proc eq*(a, b: VNode): bool =
+  if a.track != 0 and b.track != 0:
+    # do not recurse here:
+    return a.track == b.track
   if a.kind != b.kind: return false
   if a.id != b.id: return false
   if a.class != b.class: return false
@@ -146,7 +151,11 @@ proc eq*(a, b: VNode): bool =
 
 proc setAttr*(n: VNode; key: cstring; val: cstring = "") =
   if n.attrs.isNil:
-    n.attrs = @[key, val]
+    when true:
+      let x = @[key, val]
+      shallowCopy n.attrs, x
+    else:
+      n.attrs = @[key, val]
   else:
     for i in countup(0, n.attrs.len-2, 2):
       if n.attrs[i] == key:
@@ -161,6 +170,7 @@ proc getAttr*(n: VNode; key: cstring): cstring =
 
 proc len*(x: VNode): int = x.kids.len
 proc `[]`*(x: VNode; idx: int): VNode = x.kids[idx]
+proc `[]=`*(x: VNode; idx: int, y: VNode) = x.kids[idx] = y
 proc add*(parent, kid: VNode) = parent.kids.add kid
 proc newVNode*(kind: VNodeKind): VNode = VNode(kind: kind, key: -1)
 
@@ -216,32 +226,33 @@ proc toString*(n: VNode; result: var string; indent: int) =
   for i in 1..indent: result.add ' '
   result.add "\L</" & $n.kind & ">"
 
-proc calcHash*(n: VNode) =
-  if n.validHash: return
-  n.validHash = true
-  var h: Hash = ord n.kind
-  if n.id != nil:
-    h &= "id"
-    h &= n.id
-  if n.class != nil:
-    h &= "class"
-    h &= n.class
-  if n.key >= 0:
-    h &= "k"
-    h &= n.key
-  for k, v in attrs(n):
-    h &= " "
-    h &= k
-    h &= "="
-    h &= v
-  if n.kind == VNodeKind.text or n.text != nil:
-    h &= "t"
-    h &= n.text
-  else:
-    for child in items(n):
-      calcHash(child)
-      h &= child.hash
-  n.hash = h
+when false:
+  proc calcHash*(n: VNode) =
+    if n.validHash: return
+    n.validHash = true
+    var h: Hash = ord n.kind
+    if n.id != nil:
+      h &= "id"
+      h &= n.id
+    if n.class != nil:
+      h &= "class"
+      h &= n.class
+    if n.key >= 0:
+      h &= "k"
+      h &= n.key
+    for k, v in attrs(n):
+      h &= " "
+      h &= k
+      h &= "="
+      h &= v
+    if n.kind == VNodeKind.text or n.text != nil:
+      h &= "t"
+      h &= n.text
+    else:
+      for child in items(n):
+        calcHash(child)
+        h &= child.hash
+    n.hash = h
 
 proc `$`*(n: VNode): cstring =
   var res = ""
diff --git a/uibench/index.html b/uibench/index.html
new file mode 100644
index 0000000..5b2cb4c
--- /dev/null
+++ b/uibench/index.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <link href="https://localvoid.github.io/uibench-base/0.1.0/styles.css" rel="stylesheet" />
+  <title>UI Benchmark: React</title>
+</head>
+<body>
+
+<div id="ROOT"></div>
+
+<script src="https://localvoid.github.io/uibench-base/0.1.0/uibench.js"></script>
+<script src="nimcache/nim_uibench.js" type="text/javascript"></script>
+
+</body>
+</html>
diff --git a/uibench/nim_uibench.nim b/uibench/nim_uibench.nim
new file mode 100644
index 0000000..764d1db
--- /dev/null
+++ b/uibench/nim_uibench.nim
@@ -0,0 +1,106 @@
+import dom, vdom, karax, karaxdsl, jdict, jstrutils, kajax
+
+type
+    HomeState {.importc.} = ref object
+    TableItemState {.importc.} = ref object
+        id: int
+        active: bool
+        props: seq[cstring]
+    TableState {.importc.} = ref object
+        items: seq[TableItemState]
+    AnimBoxState {.importc.} = ref object
+        id: int
+        time: int
+    AnimState {.importc.} = ref object
+        items: seq[AnimBoxState]
+    TreeNodeState {.importc.} = ref object
+        id: int
+        container: bool
+        children: seq[TreeNodeState]
+    TreeState {.importc.} = ref object
+        root: TreeNodeState
+    AppState {.importc.} = ref object
+        location: cstring
+        home: HomeState
+        table: TableState
+        anim: AnimState
+        tree: TreeState
+
+var appState: AppState
+
+proc createTableCell(id: cstring): VNode =
+    proc tableCellClick(ev: karax.Event; n: VNode) =
+        kout "Clicked" & id
+    result = buildHtml(td(class="TableCell", onclick=tableCellClick)):
+        text id
+
+proc createTableRow(item: TableItemState): VNode =
+    let className = if item.active: cstring"TableRow active" else: cstring"TableRow"
+    result = buildHtml(tr(class=className, `data-id` = &item.id, track = item.id)):
+        createTableCell("#" & &item.id)
+        for i in 0..<len(item.props):
+            createTableCell(item.props[i])
+
+proc tableCreateVNode(data: TableState): VNode =
+    result = buildHtml(table(class="Table")):
+        tbody:
+            for child in data.items:
+                createTableRow(child)
+
+proc createAnimBox(item: AnimBoxState): VNode =
+    let time = item.time
+    let t10 = time mod 10
+    let color = float(t10) / 10
+    let divStyles = cstring"border-radius: " & &t10 &
+         "px; background: rgba(0,0,0," & cstring($color) & ")"
+    result = flatHtml(tdiv(class="AnimBox", `data-id` = &item.id, track = item.id,
+        style=divStyles))
+
+proc animCreateVNode(data: AnimState): VNode =
+    result = buildHtml(tdiv(class="Anim")):
+        for child in data.items:
+            createAnimBox(child)
+
+proc createTreeNode(data: TreeNodeState): VNode =
+    result = buildHtml(ul(class="TreeNode")):
+        for n in data.children:
+            if n.container:
+                createTreeNode(n)
+            else:
+                li(class="TreeLeaf"):
+                    text &n.id
+
+proc treeCreateVNode(data: TreeState): VNode =
+    result = buildHtml(tdiv(class="Tree")):
+        createTreeNode(data.root)
+
+proc update(): VNode =
+    assert appState != nil
+    let location = appState.location
+    var children: VNode = nil
+    if location == cstring"table":
+        children = tableCreateVNode(appState.table)
+    elif location == cstring"anim":
+        children = animCreateVNode(appState.anim)
+    elif location == cstring"tree":
+        children = treeCreateVNode(appState.tree)
+    result = buildHtml():
+        tdiv(class="Main"):
+            children
+
+proc a(state: AppState) =
+    appState = state
+    redrawForce()
+
+proc myToJson[T](x: T): cstring {.importcpp: "JSON.stringify(#, null, ' ')".}
+
+proc b(samples: RootRef) =
+    document.body.innerHTML = cstring"<pre>" & myToJson(samples) & cstring"</pre>"
+
+proc init*(a: cstring, b: cstring) {.importc: "uibench.init", nodecl.}
+proc run*(a: proc(state: AppState), b: proc(samples: RootRef)) {.importc: "uibench.run", nodecl.}
+
+init(cstring"Nim-karax", cstring"0.6.1")
+
+setRendererOnly update
+run(a, b)
\ No newline at end of file
diff --git a/uibench/nim_uibench.nims b/uibench/nim_uibench.nims
new file mode 100644
index 0000000..532b206
--- /dev/null
+++ b/uibench/nim_uibench.nims
@@ -0,0 +1 @@
+--path: "../src"