diff --git a/src/JSONEditor.svelte b/src/JSONEditor.svelte
index 2d871ce..1e6e53a 100644
--- a/src/JSONEditor.svelte
+++ b/src/JSONEditor.svelte
@@ -1,4 +1,5 @@
 <script>
+  import { EXPANDED_PROPERTY } from './constants.js'
   import SearchBox from './SearchBox.svelte'
   import Icon from 'svelte-awesome'
   import { faSearch, faUndo, faRedo } from '@fortawesome/free-solid-svg-icons'
@@ -14,6 +15,10 @@
   export let onChangeJson = () => {
   }
 
+  let state = {
+    [EXPANDED_PROPERTY]: true
+  }
+
   let showSearch = true // FIXME: change to false
   let searchText = ''
 
@@ -33,10 +38,19 @@
     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 patchResult = immutableJSONPatch(json, operations)
+    const patchResult = applyPatch(operations)
 
     history.add({
       undo: patchResult.revert,
@@ -123,7 +137,7 @@
     if (history.getState().canUndo) {
       const item = history.undo()
       if (item) {
-        json = immutableJSONPatch(json, item.undo).json
+        applyPatch(item.undo)
         emitOnChange()
       }
     }
@@ -133,12 +147,21 @@
     if (history.getState().canRedo) {
       const item = history.redo()
       if (item) {
-        json = immutableJSONPatch(json, item.redo).json
+        applyPatch(item.redo)
         emitOnChange()
       }
     }
   }
 
+  /**
+   * Toggle expanded state of a node
+   * @param {Path} path
+   * @param {boolean} expanded
+   */
+  function handleExpand (path, expanded) {
+    state = setIn(state, path.concat(EXPANDED_PROPERTY), expanded)
+  }
+
   function handleKeyDown (event) {
     const combo = keyComboFromEvent(event)
 
@@ -228,10 +251,11 @@
   <div class="contents">
     <Node
       value={json}
+      state={state}
       searchResult={searchResultWithActive}
-      expanded={true}
       onChangeKey={handleChangeKey}
       onPatch={handlePatch}
+      onExpand={handleExpand}
       getParentPath={getPath}
     />
     <div class='bottom'></div>
diff --git a/src/JSONNode.svelte b/src/JSONNode.svelte
index 3dda4a5..001e199 100644
--- a/src/JSONNode.svelte
+++ b/src/JSONNode.svelte
@@ -1,8 +1,12 @@
 <script>
+  import {
+    EXPANDED_PROPERTY,
+    SEARCH_PROPERTY,
+    SEARCH_VALUE
+  } from './constants.js'
   import { getPlainText, setPlainText } from './utils/domUtils.js'
   import Icon from 'svelte-awesome'
   import { faCaretDown, faCaretRight } from '@fortawesome/free-solid-svg-icons'
-  import { SEARCH_PROPERTY, SEARCH_VALUE } from './utils/search.js'
   import classnames from 'classnames'
   import debounce from 'lodash/debounce'
   import { findUniqueName } from './utils/stringUtils.js'
@@ -12,13 +16,16 @@
 
   export let key = undefined // only applicable for object properties
   export let value
+  export let state
   export let searchResult
   export let onPatch
   export let onChangeKey
-  export let expanded = false
+  export let onExpand
 
   export let getParentPath
 
+  $: expanded = state && state[EXPANDED_PROPERTY]
+
   function getPath () {
     return key !== undefined
       ? getParentPath().concat(key)
@@ -93,7 +100,7 @@
   }
 
   function toggle () {
-    expanded = !expanded
+    onExpand(getPath(), !expanded)
   }
 
   function updateKey () {
@@ -238,7 +245,7 @@
         <div class="delimiter">[</div>
       {:else}
         <div class="delimiter">[</div>
-        <button class="tag" on:click={() => expanded = true}>{value.length} items</button>
+        <button class="tag" on:click={() => onExpand(getPath(), true)}>{value.length} items</button>
         <div class="delimiter">]</div>
       {/if}
     </div>
@@ -248,9 +255,11 @@
           <svelte:self
             key={index}
             value={item}
+            state={state && state[index]}
             searchResult={searchResult ? searchResult[index] : undefined}
             onChangeKey={handleChangeKey}
             onPatch={onPatch}
+            onExpand={onExpand}
             getParentPath={getPath}
           />
         {/each}
@@ -288,7 +297,7 @@
         <span class="delimiter">&#123;</span>
       {:else}
         <span class="delimiter"> &#123;</span>
-        <button class="tag" on:click={() => expanded = true}>{props.length} props</button>
+        <button class="tag" on:click={() => onExpand(getPath(), true)}>{props.length} props</button>
         <span class="delimiter">}</span>
       {/if}
     </div>
@@ -298,9 +307,11 @@
           <svelte:self
             key={prop.key}
             value={value[prop.key]}
+            state={state && state[prop.key]}
             searchResult={searchResult ? searchResult[prop.key] : undefined}
             onChangeKey={handleChangeKey}
             onPatch={onPatch}
+            onExpand={onExpand}
             getParentPath={getPath}
           />
         {/each}
diff --git a/src/constants.js b/src/constants.js
new file mode 100644
index 0000000..697b1a6
--- /dev/null
+++ b/src/constants.js
@@ -0,0 +1,5 @@
+
+export const EXPANDED_PROPERTY = '$jse:expanded'
+export const SEARCH_PROPERTY = '$jse:search:property'
+export const SEARCH_VALUE = '$jse:search:value'
+
diff --git a/src/types.js b/src/types.js
index 395d665..9ae72f3 100644
--- a/src/types.js
+++ b/src/types.js
@@ -25,7 +25,7 @@
  */
 
 /**
- * @typedef {string[]} Path
+ * @typedef {<string | number>[]} Path
  */
 
 /**
diff --git a/src/utils/immutabilityHelpers.js b/src/utils/immutabilityHelpers.js
index 75d6631..f354b23 100644
--- a/src/utils/immutabilityHelpers.js
+++ b/src/utils/immutabilityHelpers.js
@@ -70,12 +70,22 @@ export function setIn (object, path, value) {
     return value
   }
 
-  if (!isObjectOrArray(object)) {
-    throw new Error('Path does not exist')
-  }
+  // TODO: rewrite this function into a while loop instead of recursive (like getIn)
 
   const key = path[0]
-  const updatedValue = setIn(object[key], path.slice(1), value)
+
+  // TODO: check whether path is string -> object expected, path is number -> array expected
+
+  const updatedValue = setIn(object && object[key], path.slice(1), value)
+
+  if (!isObjectOrArray(object)) {
+    const newObject = typeof key === 'number'
+      ? []
+      : {}
+    newObject[key] = updatedValue
+    return newObject
+  }
+
   if (object[key] === updatedValue) {
     // return original object unchanged when the new value is identical to the old one
     return object
diff --git a/src/utils/immutabilityHelpers.test.js b/src/utils/immutabilityHelpers.test.js
index e902628..1a096e6 100644
--- a/src/utils/immutabilityHelpers.test.js
+++ b/src/utils/immutabilityHelpers.test.js
@@ -59,19 +59,32 @@ test('setIn basic', () => {
   expect(obj).not.toBe(updated)
 })
 
-test('setIn non existing path', () => {
+test('setIn non existing path should create the path (1)', () => {
   const obj = {}
 
-  expect(() => setIn(obj, ['a', 'b', 'c'], 4)).toThrow(/Path does not exist/)
+  expect(setIn(obj, ['a', 'b', 'c'], 4)).toEqual({
+    a: {
+      b: {
+        c: 4
+      }
+    }
+  })
 })
 
-test('setIn replace value with object should throw an exception', () => {
+test('setIn on non-existing path should create the path (2)', () => {
   const obj = {
     a: 42,
     d: 3
   }
 
-  expect(()  => setIn(obj, ['a', 'b', 'c'], 4)).toThrow(/Path does not exist/)
+  expect(setIn(obj, ['a', 'b', 'c'], 4)).toEqual({
+    a: {
+      b: {
+        c: 4
+      }
+    },
+    d: 3
+  })
 })
 
 test('setIn replace value inside nested array', () => {
diff --git a/src/utils/search.js b/src/utils/search.js
index f480828..30746ce 100644
--- a/src/utils/search.js
+++ b/src/utils/search.js
@@ -1,8 +1,6 @@
+import { SEARCH_PROPERTY, SEARCH_VALUE } from '../constants.js'
 import { valueType } from './typeUtils.js'
 
-export const SEARCH_PROPERTY = '$jse:search:property'
-export const SEARCH_VALUE = '$jse:search:value'
-
 export function search (key, value, searchText) {
   let results = undefined