diff --git a/diffDomTests.html b/diffDomTests.html
new file mode 100644
index 0000000..5ecf130
--- /dev/null
+++ b/diffDomTests.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+
+<html>
+<head>
+  <title>Diff dom tests</title>
+  <link rel="stylesheet" href="style.css">
+</head>
+
+<body id="body">
+
+<div id="ROOT" />
+
+<script type="text/javascript" src="nimcache/diffDomTests.js"></script>
+<script type="text/javascript">
+  onload(window.location.pathname.split('/')[1])
+</script>
+
+</body>
+</html>
diff --git a/diffDomTests.nim b/diffDomTests.nim
new file mode 100644
index 0000000..fe808f6
--- /dev/null
+++ b/diffDomTests.nim
@@ -0,0 +1,178 @@
+
+import vdom, times, karax, karaxdsl, jdict, jstrutils, parseutils, sequtils
+
+var
+    entries: seq[cstring]
+    timeout : Timeout
+
+proc reset() =
+    kout cstring"reset started"
+    entries = @[cstring("0"), cstring("1"), cstring("2"), cstring("3"), cstring("4"), cstring("5") ]
+    redraw()
+    kout cstring"reset finished"
+
+proc checkOrder(order : seq[int]): bool = 
+    var ul = getElementById("ul")
+    if ul == nil or len(ul.children) != len(order):
+        return false
+    var pos = 0
+    for child in ul.children:
+        if child.id != $order[pos]:
+            return false
+        inc pos
+    return true
+
+proc check1() =
+    let result = checkOrder(@[0, 1, 2, 3, 4, 7, 5])
+    if result:
+        kout cstring"test1 - OK"
+    else:
+        kout cstring"test1 - FAIL"
+
+# result: 0 1 2 3 4 7 5
+proc test1() =
+    kout cstring"test1 started"
+    entries = @[cstring("0"), cstring("1"), cstring("2"), cstring("3"), cstring("4"), cstring("5") ]
+    entries.insert(cstring("7"), 5)
+    redraw()
+    timeout = setTimeout(check1, 20)
+
+proc check2() =
+    let result = checkOrder(@[8, 0, 1, 2, 3, 4, 7, 5])
+    if result:
+        kout cstring"test1 - OK"
+    else:
+        kout cstring"test2 - FAIL"
+
+# result: 8 0 1 2 3 4 7 5
+proc test2() =
+    kout cstring"test2 started"
+    entries = @[cstring("0"), cstring("1"), cstring("2"), cstring("3"), cstring("4"), cstring("5") ]
+    entries.insert(cstring("7"), 5)
+    entries.insert(cstring("8"), 0)
+    redraw()
+    timeout = setTimeout(check2, 20)
+
+proc check3() =
+    let result = checkOrder(@[2, 3, 4, 1])
+    if result:
+        kout cstring"test3 - OK"
+    else:
+        kout cstring"test3 - FAIL"
+
+# result: 2 3 4 1
+proc test3() =
+    kout cstring"test3 started"
+    entries = @[cstring("2"), cstring("3"), cstring("4"), cstring("1") ]
+    redraw()
+    timeout = setTimeout(check3, 20)
+
+proc check4() =
+    let result = checkOrder(@[5, 6, 7, 8])
+    if result:
+        kout cstring"test4 - OK"
+    else:
+        kout cstring"test4 - FAIL"
+
+# result: 5 6 7 8
+proc test4() =
+    kout cstring"test4 started"
+    entries = @[cstring("5"), cstring("6"), cstring("7"), cstring("8") ]
+    redraw()
+    timeout = setTimeout(check4, 20)
+
+proc check5() =
+    let result = checkOrder(@[0, 1, 3, 5, 4, 5])
+    if result:
+        kout cstring"test5 - OK"
+    else:
+        kout cstring"test5 - FAIL"
+
+# result: 0 1 3 5 4 5
+proc test5() =
+    kout cstring"test5 started"
+    entries = @[cstring("0"), cstring("1"), cstring("3"), cstring("5"), cstring("4"), cstring("5") ]
+    redraw()
+    timeout = setTimeout(check5, 20)
+     
+proc check6() =
+    let result = checkOrder(@[])
+    if result:
+        kout cstring"test6 - OK"
+    else:
+        kout cstring"test6 - FAIL"
+
+# result: empty
+proc test6() =
+    kout cstring"test6 started"
+    entries = @[]
+    redraw()
+    timeout = setTimeout(check6, 20)
+
+proc check7() =
+    let result = checkOrder(@[2])
+    if result:
+        kout cstring"test7 - OK"
+    else:
+        kout cstring"test7 - FAIL"
+
+# result: 2
+proc test7() =
+    kout cstring"test7 started"
+    entries = @[cstring("2")]
+    redraw()
+    timeout = setTimeout(check7, 20)
+    
+proc createEntry(id: int): VNode =
+  result = buildHtml():
+    button(id="" & $id):
+        text $id
+
+proc createDom(): VNode =
+    result = buildHtml(tdiv()):
+        ul(id="ul"):
+            for e in entries:
+                createEntry(parseInt(e)) 
+                
+setRenderer createDom
+
+proc onload(session: cstring) {.exportc.} =
+    for i in 0..5: # 0_000:
+        entries.add(cstring($i))
+    init()
+
+    var dtReset = 100
+    var dtTest = 500
+
+    var t = dtReset
+    timeout = setTimeout(test1, t)
+    t += dtTest
+    timeout = setTimeout(reset, t)
+    t += dtReset
+
+    timeout = setTimeout(test2, t)
+    t += dtTest
+    timeout = setTimeout(reset, t)
+    t += dtReset
+
+    timeout = setTimeout(test3, t)
+    t += dtTest
+    timeout = setTimeout(reset, t)
+    t += dtReset
+
+    timeout = setTimeout(test4, t)
+    t += dtTest
+    timeout = setTimeout(reset, t)
+    t += dtReset
+
+    timeout = setTimeout(test5, t)
+    t += dtTest
+    timeout = setTimeout(reset, t)
+    t += dtReset
+
+    timeout = setTimeout(test6, t)
+    t += dtTest
+    timeout = setTimeout(reset, t)
+    t += dtReset
+
+    timeout = setTimeout(test7, t)
diff --git a/karax.nim b/karax.nim
index 5858f36..fb3003e 100644
--- a/karax.nim
+++ b/karax.nim
@@ -117,7 +117,7 @@ proc setTimeout*(action: proc(); ms: int): Timeout {.importc, nodecl.}
 proc clearTimeout*(t: Timeout) {.importc, nodecl.}
 #proc targetElem*(e: Event): Element = cast[Element](e.target)
 
-#proc getElementById*(id: cstring): Element {.importc: "document.getElementById", nodecl.}
+proc getElementById*(id: cstring): Element {.importc: "document.getElementById", nodecl.}
 
 #proc getElementsByClassName*(cls: cstring): seq[Element] {.importc:
 #  "document.getElementsByClassName", nodecl.}
@@ -147,6 +147,13 @@ proc equals(a, b: VNode): bool =
   # --> maybe give nodes a hash?
   return true
 
+proc equalsTree(a, b: VNode): bool =
+  if not a.validHash:
+    a.calcHash()
+  if not b.validHash:
+    b.calcHash()
+  return a.hash == b.hash
+
 proc updateElement(parent, current: Node, newNode, oldNode: VNode) =
   if not equals(newNode, oldNode):
     let n = vnodeToDom(newNode)
@@ -156,21 +163,49 @@ proc updateElement(parent, current: Node, newNode, oldNode: VNode) =
       parent.replaceChild(n, current)
   elif newNode.kind != VNodeKind.text:
     let newLength = newNode.len
-    let oldLength = oldNode.len
+    var oldLength = oldNode.len
+    let minLength = min(newLength, oldLength)
     assert oldNode.kind == newNode.kind
-    when false:
-      if current.nodeName != toTag[oldNode.kind]:
-        kout current.nodeName
-        kout toTag[oldNode.kind]
-        assert false
-    for i in 0..min(newLength, oldLength)-1:
-      updateElement(current, current[i], newNode[i], oldNode[i])
-    if newLength > oldLength:
-      for i in oldLength..newLength-1:
-        current.appendChild(vnodeToDom(newNode[i]))
-    elif oldLength > newLength:
-      for i in countdown(oldLength-1, newLength):
-        current.removeChild(current.lastChild)
+    when defined(simpleDiff):
+      for i in 0..min(newLength, oldLength)-1:
+        updateElement(current, current[i], newNode[i], oldNode[i])
+      if newLength > oldLength:
+        for i in oldLength..newLength-1:
+          current.appendChild(vnodeToDom(newNode[i]))
+      elif oldLength > newLength:
+        for i in countdown(oldLength-1, newLength):
+          current.removeChild(current.lastChild)
+    else:
+      var commonPrefix = 0
+      while commonPrefix < minLength and equalsTree(newNode[commonPrefix], oldNode[commonPrefix]):
+        inc commonPrefix
+
+      var oldPos = oldLength - 1
+      var newPos = newLength - 1
+      while oldPos >= commonPrefix and newPos >= commonPrefix and equalsTree(newNode[newPos], oldNode[oldPos]):
+        dec oldPos
+        dec newPos
+
+      var pos = min(oldPos, newPos) + 1
+      for i in commonPrefix..pos-1:
+        updateElement(current, current.childNodes[i],
+          newNode[i],
+          oldNode[i])
+
+      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
+
+      for i in 0..oldPos-pos:
+        current.removeChild(current.childNodes[pos])
+
 
 proc dodraw() =
   let newtree = dorender()
@@ -187,7 +222,7 @@ proc dodraw() =
     currentTree = newtree
   # now that it's part of the DOM, give it the focus:
   if toFocus != nil:
-    toFocus.focus()
+    discard "toFocus.focus()"
 
 proc visibleKeys(e: Node; a, b: var VKey; h, count: var int) =
   # we only care about nodes that have a key:
diff --git a/scrollapp.nim b/scrollapp.nim
index f3b70b2..7b7ce8e 100644
--- a/scrollapp.nim
+++ b/scrollapp.nim
@@ -90,6 +90,9 @@ proc lazyEntry(args: seq[VNode]): VNode =
 proc createEntry(id: int; d: cstring; completed, selected: bool): VNode =
   result = thunk(lazyEntry, id, d, completed, selected)
 
+proc myscroll(ev: Event; n: VNode) =
+  kout cstring"scrolling event here"
+
 proc createDom(): VNode =
   result = buildHtml(tdiv(class="todomvc-wrapper")):
     section(class = "todoapp"):
@@ -102,6 +105,11 @@ proc createDom(): VNode =
         input(class = "toggle-all", `type` = "checkbox", name = "toggle")
         label(`for` = "toggle-all", onclick = onAllDone):
           text "Mark all as complete"
+        tdiv(onscroll = myscroll, style = "overflow: visible; width: 0px; display: block; max-height: 1em"):
+          for i in 0..4:
+            tdiv:
+              text entries[i][0]
+
         var entriesCount = 0
         var completedCount = 0
         ul(class = "todo-list"):
diff --git a/todoapp.nim b/todoapp.nim
index 63875a6..ea71c66 100644
--- a/todoapp.nim
+++ b/todoapp.nim
@@ -119,3 +119,6 @@ proc onload(session: cstring) {.exportc.} =
   for i in 0..1: # 0_000:
     entries.add((cstring"Entry " & &i, false))
   init()
+
+for i in 0..10_000:
+    entries.add((cstring"Entry " & &i, false))
\ No newline at end of file
diff --git a/vdom.nim b/vdom.nim
index ba1202d..0ddfc3a 100644
--- a/vdom.nim
+++ b/vdom.nim
@@ -1,6 +1,7 @@
 # Virtual DOM implementation
 
 from dom import Event
+import shash
 
 type
   VNodeKind* {.pure.} = enum
@@ -43,6 +44,8 @@ type
     attrs: seq[cstring]
     events*: seq[(EventKind, EventHandler)]
     thunk*: proc (args: seq[VNode]): VNode
+    hash*: Hash
+    validHash*: bool
 
 proc value*(n: VNode): cstring = n.text
 proc `value=`*(n: VNode; v: cstring) = n.text = v
@@ -146,6 +149,33 @@ 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
+
 proc `$`*(n: VNode): cstring =
   var res = ""
   toString(n, res, 0)