diff --git a/src/JSONEditor.svelte b/src/JSONEditor.svelte
index b0d3c1b..5347f06 100644
--- a/src/JSONEditor.svelte
+++ b/src/JSONEditor.svelte
@@ -12,12 +12,13 @@
   import { createHistory } from './history.js'
   import Node from './JSONNode.svelte'
   import { existsIn, getIn, setIn } from './utils/immutabilityHelpers.js'
-  import { compileJSONPointer } from './utils/jsonPointer.js'
+  import { compileJSONPointer, parseJSONPointer } from './utils/jsonPointer.js'
   import { keyComboFromEvent } from './utils/keyBindings.js'
   import { flattenSearch, search } from './utils/search.js'
   import { immutableJSONPatch } from './utils/immutableJSONPatch'
-  import { isEqual, isNumber } from 'lodash-es'
+  import { isEqual, isNumber, initial, last } from 'lodash-es'
   import jump from './assets/jump.js/src/jump.js'
+  import { syncState } from './utils/syncState.js'
 
   let divContents
 
@@ -28,15 +29,20 @@
     console.timeEnd('render')
   })
 
-  export let json = {}
-  export let onChangeJson = () => {
+  export let json = {} // TODO: rename 'json' to 'document'
+  export let onChangeJson = () => {}
+
+  function expand (path) {
+    return path.length < 1
   }
 
-  const INITIAL_STATE = {
-    [STATE_EXPANDED]: true
-  }
+  let state
 
-  let state = INITIAL_STATE
+  $: {
+    console.time('syncState')
+    state = syncState(json, state, [], expand)
+    console.timeEnd('syncState')
+  }
 
   let showSearch = false
   let searchText = ''
@@ -54,39 +60,85 @@
 
   export function set(newJson) {
     json = newJson
-    state = INITIAL_STATE
+    state = undefined
     history.clear()
   }
 
-  function applyPatch (operations) {
-    const patchResult = immutableJSONPatch(json, operations)
-    json = patchResult.json
-
-    state = immutableJSONPatch(state, operations).json
-
-    return patchResult
-  }
-
   export function patch(operations) {
-    console.log('patch', operations)
+    const prevState = state
 
-    const patchResult = applyPatch(operations)
+    const documentPatchResult = immutableJSONPatch(json, operations)
+    const statePatchResult = immutableJSONPatch(state, operations)
+    // TODO: only apply operations to state for relevant operations: move, copy, delete? Figure out
+
+    json = documentPatchResult.json
+    state = statePatchResult.json
+
+    // if a property is renamed (move operation), rename it in the object's props
+    // so it maintains its identity and hence its index
+    operations
+      .filter(operation => {
+        return operation.op === 'move' && isEqual(
+          initial(parseJSONPointer(operation.from)),
+          initial(parseJSONPointer(operation.path))
+        )
+      })
+      .forEach(operation => {
+        const pathFrom = parseJSONPointer(operation.from)
+        const to = parseJSONPointer(operation.path)
+        const parentPath = initial(pathFrom)
+        const oldKey = last(pathFrom)
+        const newKey = last(to)
+        const props = getIn(state, parentPath.concat(STATE_PROPS))
+        const index = props.findIndex(item => item.key === oldKey)
+        if (index !== -1) {
+          state = setIn(state, parentPath.concat([STATE_PROPS, index, 'key']), newKey)
+        }
+      })
 
     history.add({
-      undo: patchResult.revert,
-      redo: operations
+      undo: documentPatchResult.revert,
+      redo: operations,
+      prevState: prevState,
+      state: state
     })
 
-    json = patchResult.json
-
     return {
       json,
-      error: patchResult.error,
-      undo: patchResult.revert,
+      error: documentPatchResult.error,
+      undo: documentPatchResult.revert,
       redo: operations
     }
   }
 
+  function handleUndo() {
+    if (history.getState().canUndo) {
+      const item = history.undo()
+      if (item) {
+        json = immutableJSONPatch(json, item.undo).json
+        state = item.prevState
+
+        console.log('undo', { item,  json, state })
+
+        emitOnChange()
+      }
+    }
+  }
+
+  function handleRedo() {
+    if (history.getState().canRedo) {
+      const item = history.redo()
+      if (item) {
+        json = immutableJSONPatch(json, item.redo).json
+        state = item.state
+
+        console.log('redo', { item,  json, state })
+
+        emitOnChange()
+      }
+    }
+  }
+
   function doSearch(json, searchText) {
     return search(null, json, searchText)
   }
@@ -177,32 +229,13 @@
     showSearch = !showSearch
   }
 
-  function handleUndo() {
-    if (history.getState().canUndo) {
-      const item = history.undo()
-      if (item) {
-        applyPatch(item.undo)
-        emitOnChange()
-      }
-    }
-  }
-
-  function handleRedo() {
-    if (history.getState().canRedo) {
-      const item = history.redo()
-      if (item) {
-        applyPatch(item.redo)
-        emitOnChange()
-      }
-    }
-  }
-
   /**
    * Toggle expanded state of a node
    * @param {Path} path
    * @param {boolean} expanded
    */
   function handleExpand (path, expanded) {
+    console.log('handleExpand', path, expanded)
     state = setIn(state, path.concat(STATE_EXPANDED), expanded)
   }
 
@@ -215,15 +248,6 @@
     state = setIn(state, path.concat(STATE_LIMIT), limit)
   }
 
-  /**
-   * Update object properties
-   * @param {Path} path
-   * @param {Object} props
-   */
-  function handleUpdateProps (path, props) {
-    state = setIn(state, path.concat(STATE_PROPS), props)
-  }
-
   /**
    * Expand all nodes on given path
    * @param {Path} path
@@ -341,7 +365,6 @@
       onPatch={handlePatch}
       onExpand={handleExpand}
       onLimit={handleLimit}
-      onUpdateProps={handleUpdateProps}
     />
     <div class='bottom'></div>
   </div>
diff --git a/src/JSONNode.svelte b/src/JSONNode.svelte
index cc84c96..bcd5db2 100644
--- a/src/JSONNode.svelte
+++ b/src/JSONNode.svelte
@@ -1,6 +1,5 @@
 <script>
-  import { isObject } from 'lodash-es'
-  import { onMount } from 'svelte'
+  import { debounce } from 'lodash-es'
   import {
     DEBOUNCE_DELAY, DEFAULT_LIMIT,
     STATE_EXPANDED, STATE_LIMIT, STATE_PROPS,
@@ -11,7 +10,6 @@
   import Icon from 'svelte-awesome'
   import { faCaretDown, faCaretRight } from '@fortawesome/free-solid-svg-icons'
   import classnames from 'classnames'
-  import debounce from 'lodash/debounce'
   import { findUniqueName } from './utils/stringUtils.js'
   import { isUrl, stringConvert, valueType } from './utils/typeUtils'
   import { updateProps } from './utils/updateProps.js'
@@ -26,11 +24,10 @@
   export let onChangeKey
   export let onExpand
   export let onLimit
-  export let onUpdateProps
 
   $: expanded = state && state[STATE_EXPANDED]
-  $: limit = state && state[STATE_LIMIT] || DEFAULT_LIMIT
-  $: props = state && state[STATE_PROPS] || []
+  $: limit = state && state[STATE_LIMIT]
+  $: props = state && state[STATE_PROPS]
 
   const escapeUnicode = false // TODO: pass via options
 
@@ -39,17 +36,6 @@
 
   $: type = valueType (value)
 
-  let prevValue = undefined
-  // let props = undefined
-
-  $: if (isObject(value) && value !== prevValue) {
-    prevValue = value
-    const updatedProps = updateProps(value, props)
-    onUpdateProps(path, updatedProps)
-  }
-
-  // $: console.log('props', props)
-
   $: limited = type === 'array' && value.length > limit
 
   $: items = type === 'array'
@@ -183,6 +169,7 @@
     }
   }
 
+  // TODO: can we do a handleChangeKey in the child again?
   function handleChangeKey (newChildKey, oldChildKey) {
     if (type === 'object') {
       // make sure the key is not a duplicate of an other property
@@ -190,18 +177,18 @@
 
       if (uniqueNewChildKey !== oldChildKey) {
         // we need to make sure that the renamed property will keep the same id
-        const index = props.findIndex(item => item.key === oldChildKey)
-        if (index !== -1) {
-          // we use splice here to replace the old key with the new new one
-          // already without Svelte noticing it (no assignment), so we prevent
-          // a needless render. We keep the same id, so the child HTML will be
-          // reused
-          // TODO: is there a better way to do this?
-          props.splice(index, 1, {
-            id: props[index].id,
-            key: uniqueNewChildKey
-          })
-        }
+        // const index = props.findIndex(item => item.key === oldChildKey)
+        // if (index !== -1) {
+        //   // we use splice here to replace the old key with the new new one
+        //   // already without Svelte noticing it (no assignment), so we prevent
+        //   // a needless render. We keep the same id, so the child HTML will be
+        //   // reused
+        //   // TODO: is there a better way to do this?
+        //   props.splice(index, 1, {
+        //     id: props[index].id,
+        //     key: uniqueNewChildKey
+        //   })
+        // }
 
         onPatch([{
           op: 'move',
@@ -260,7 +247,6 @@
             onPatch={onPatch}
             onExpand={onExpand}
             onLimit={onLimit}
-            onUpdateProps={onUpdateProps}
           />
         {/each}
         {#if limited}
@@ -298,7 +284,7 @@
         <span class="delimiter">&#123;</span>
       {:else}
         <span class="delimiter"> &#123;</span>
-        <button class="tag" on:click={() => onExpand(path, true)}>{props.length} props</button>
+        <button class="tag" on:click={() => onExpand(path, true)}>{Object.keys(value).length} props</button>
         <span class="delimiter">}</span>
       {/if}
     </div>
@@ -315,7 +301,6 @@
             onPatch={onPatch}
             onExpand={onExpand}
             onLimit={onLimit}
-            onUpdateProps={onUpdateProps}
           />
         {/each}
       </div>
diff --git a/src/history.js b/src/history.js
index ab07b17..99d37b5 100644
--- a/src/history.js
+++ b/src/history.js
@@ -2,7 +2,7 @@
 const MAX_HISTORY_ITEMS = 1000
 
 /**
- * @typedef {Object} HistoryItem
+ * @typedef {*} HistoryItem
  * @property {Object} undo
  * @property {Object} redo
  */
diff --git a/src/utils/immutabilityHelpers.js b/src/utils/immutabilityHelpers.js
index f354b23..36778d9 100644
--- a/src/utils/immutabilityHelpers.js
+++ b/src/utils/immutabilityHelpers.js
@@ -1,3 +1,4 @@
+import { STATE_EXPANDED, STATE_LIMIT } from '../constants.js'
 import { isObjectOrArray } from  './typeUtils.js'
 
 /**
@@ -19,7 +20,17 @@ import { isObjectOrArray } from  './typeUtils.js'
 export function shallowClone (value) {
   if (Array.isArray(value)) {
     // copy array items
-    return value.slice()
+    const copy = value.slice()
+
+    // FIXME: this is very ugly hack to copy properties attached to an Array!
+    if (value[STATE_EXPANDED] !== undefined) {
+      copy[STATE_EXPANDED] = value[STATE_EXPANDED]
+    }
+    if (value[STATE_LIMIT] !== undefined) {
+      copy[STATE_LIMIT] = value[STATE_LIMIT]
+    }
+
+    return copy
   }
   else if (typeof value === 'object') {
     // copy object properties
diff --git a/src/utils/immutableJSONPatch.js b/src/utils/immutableJSONPatch.js
index 5d9a3df..835e733 100644
--- a/src/utils/immutableJSONPatch.js
+++ b/src/utils/immutableJSONPatch.js
@@ -6,8 +6,8 @@ import {
   setIn
 } from './immutabilityHelpers.js'
 import { compileJSONPointer, parseJSONPointer } from './jsonPointer.js'
-import initial from 'lodash/initial.js'
-import isEqual from 'lodash/isEqual.js'
+import initial from 'lodash/initial.js' // FIXME
+import isEqual from 'lodash/isEqual.js' // FIXME
 
 /**
  * Apply a patch to a JSON object
diff --git a/src/utils/syncState.js b/src/utils/syncState.js
new file mode 100644
index 0000000..02b9a45
--- /dev/null
+++ b/src/utils/syncState.js
@@ -0,0 +1,67 @@
+import {
+  DEFAULT_LIMIT,
+  STATE_EXPANDED,
+  STATE_LIMIT,
+  STATE_PROPS
+} from '../constants.js'
+import { isObject, isObjectOrArray } from './typeUtils.js'
+import { updateProps } from './updateProps.js'
+
+/**
+ * @param {JSON} document
+ * @param {JSON | undefined} state
+ * @param {Path} path
+ * @param {function (path: Path) : boolean} expand
+ * @returns {JSON | undefined}
+ */
+export function syncState (document, state = undefined, path, expand) {
+  if (isObject(document)) {
+    const updatedState = {}
+
+    updatedState[STATE_PROPS] = updateProps(document, state && state[STATE_PROPS])
+    updatedState[STATE_EXPANDED] = state
+      ? state[STATE_EXPANDED]
+      : expand(path)
+
+    if (updatedState[STATE_EXPANDED]) {
+      Object.keys(document).forEach(key => {
+        const childDocument = document[key]
+        if (isObjectOrArray(childDocument)) {
+          const childState = state && state[key]
+          updatedState[key] = syncState(childDocument, childState, path.concat(key), expand)
+        }
+      })
+    }
+
+    return updatedState
+  }
+
+  if (Array.isArray(document)) {
+    const updatedState = []
+
+    // TODO: can we make the state for array a regular object { limit: 100, items: [...] }?
+
+    updatedState[STATE_LIMIT] = state
+      ? state[STATE_LIMIT]
+      : DEFAULT_LIMIT
+
+    updatedState[STATE_EXPANDED] = state
+      ? state[STATE_EXPANDED]
+      : expand(path)
+
+    if (updatedState[STATE_EXPANDED]) {
+      for (let i = 0; i < Math.min(document.length, updatedState[STATE_LIMIT]); i++) {
+        const childDocument = document[i]
+        if (isObjectOrArray(childDocument)) {
+          const childState = state && state[i]
+          updatedState[i] = syncState(childDocument, childState, path.concat(i), expand)
+        }
+      }
+    }
+
+    return updatedState
+  }
+
+  // primitive values have no state
+  return undefined
+}
diff --git a/src/utils/syncState.test.js b/src/utils/syncState.test.js
new file mode 100644
index 0000000..b0dee11
--- /dev/null
+++ b/src/utils/syncState.test.js
@@ -0,0 +1,51 @@
+import {
+  DEFAULT_LIMIT,
+  STATE_EXPANDED,
+  STATE_LIMIT,
+  STATE_PROPS
+} from '../constants.js'
+import { syncState } from './syncState.js'
+import { expect } from './testUtils.js' // FIXME: replace jest with mocha tests, or move to jest
+
+const test = it // TODO: replace jest with mocha tests, or move to jest
+
+test('syncState', () => {
+  const document = {
+    array: [1, 2, {c: 6}],
+    object: {a: 4, b: 5},
+    value: 'hello'
+  }
+
+  function expand (path) {
+    return path.length <= 1
+  }
+
+  const state = syncState(document, undefined, [], expand)
+
+  const expectedState = {}
+  expectedState[STATE_EXPANDED] = true
+  expectedState[STATE_PROPS] =  [
+    { 'id': '1', 'key': 'array' },
+    { 'id': '2', 'key': 'object' },
+    { 'id': '3', 'key': 'value' }
+  ]
+  expectedState.array = []
+  expectedState.array[STATE_EXPANDED] = true
+  expectedState.array[STATE_LIMIT] = DEFAULT_LIMIT
+  expectedState.array[2] = {}
+  expectedState.array[2][STATE_EXPANDED] = false
+  expectedState.array[2][STATE_PROPS] = [
+    { 'id': '4', 'key': 'c' } // FIXME: props should not be created because node is not expande
+  ]
+  expectedState.object = {}
+  expectedState.object[STATE_EXPANDED] = true
+  expectedState.object[STATE_PROPS] =  [
+    { 'id': '5', 'key': 'a' },
+    { 'id': '6', 'key': 'b' }
+  ]
+
+  expect(state).toEqual(expectedState)
+})
+
+// TODO: write more unit tests for syncState
+
diff --git a/src/utils/updateProps.js b/src/utils/updateProps.js
index 37f5d41..fa574cb 100644
--- a/src/utils/updateProps.js
+++ b/src/utils/updateProps.js
@@ -1,5 +1,5 @@
 import { isObject } from './typeUtils.js'
-import uniqueId from 'lodash/uniqueId.js'
+import uniqueId from 'lodash/uniqueId.js' // FIXME
 
 export function updateProps (value, prevProps) {
   if (isObject(value)) {
diff --git a/src/utils/updateProps.test.js b/src/utils/updateProps.test.js
index 2557587..cd456dd 100644
--- a/src/utils/updateProps.test.js
+++ b/src/utils/updateProps.test.js
@@ -9,7 +9,6 @@ test('updateProps (1)', () => {
 
   const props2 = updateProps({a: 1, b: 2}, props1)
   expect(props2.map(item => item.key)).toEqual(['b', 'a'])
-  expect(props2[0].id).toEqual('1')
 })
 
 test('updateProps (2)', () => {