diff --git a/src/components/JSONEditor.js b/src/components/JSONEditor.js
index e382ea9..9ed8cb1 100644
--- a/src/components/JSONEditor.js
+++ b/src/components/JSONEditor.js
@@ -43,7 +43,7 @@ export default class JSONEditor extends Component {
     }
   }
 
-  componentWillReceiveProps (nextProps: {mode: ?string}) {
+  componentWillReceiveProps (nextProps: {mode?: string}) {
     if (nextProps.mode !== this.props.mode) {
       this.setState({ mode: nextProps.mode })
     }
diff --git a/src/components/JSONNode.js b/src/components/JSONNode.js
index 0f0c38e..75dc4b0 100644
--- a/src/components/JSONNode.js
+++ b/src/components/JSONNode.js
@@ -165,7 +165,7 @@ export default class JSONNode extends Component {
   }
 
   // TODO: simplify the method renderProperty
-  renderProperty (prop: ?PropertyData, index: ?number, data: JSONData, options: {escapeUnicode: boolean, isPropertyEditable: (Path) => boolean}) {
+  renderProperty (prop?: PropertyData, index?: number, data: JSONData, options: {escapeUnicode: boolean, isPropertyEditable: (Path) => boolean}) {
     const isIndex = typeof index === 'number'
 
     if (!prop && !isIndex) {
@@ -325,7 +325,7 @@ export default class JSONNode extends Component {
   /**
    * Get the css style given a search result type
    */
-  static getSearchResultClass (searchResultStatus: ?SearchResultStatus) {
+  static getSearchResultClass (searchResultStatus?: SearchResultStatus) {
     if (searchResultStatus === 'active') {
       return ' jsoneditor-highlight-active'
     }
diff --git a/src/components/JSONNodeForm.js b/src/components/JSONNodeForm.js
index af353fa..77552b4 100644
--- a/src/components/JSONNodeForm.js
+++ b/src/components/JSONNodeForm.js
@@ -22,7 +22,7 @@ export default class JSONNodeForm extends JSONNode {
   }
 
   // render a readonly property
-  renderProperty (prop: ?PropertyData, index: ?number, data: JSONData, options: {escapeUnicode: boolean, isPropertyEditable: (Path) => boolean}) {
+  renderProperty (prop?: PropertyData, index?: number, data: JSONData, options: {escapeUnicode: boolean, isPropertyEditable: (Path) => boolean}) {
     const formOptions = Object.assign({}, options, { isPropertyEditable })
 
     return JSONNode.prototype.renderProperty.call(this, prop, index, data, formOptions)
diff --git a/src/jsonData.js b/src/jsonData.js
index a966a50..9e49154 100644
--- a/src/jsonData.js
+++ b/src/jsonData.js
@@ -31,7 +31,7 @@ export function expandAll (path) {
  * @param {JSONDataType} [type='value']  Optional json data type for the created value
  * @return {JSONData}
  */
-export function jsonToData (json, expand = expandAll, path = [], type = 'value') {
+export function jsonToData (json, expand = expandAll, path = [], type = 'value') : JSONData {
   if (Array.isArray(json)) {
     return {
       type: 'Array',
@@ -57,7 +57,7 @@ export function jsonToData (json, expand = expandAll, path = [], type = 'value')
       })
     }
   }
-  else {
+  else { // value
     return {
       type,
       value: json
@@ -166,7 +166,7 @@ export function expand (data: JSONData, callback: Path | (Path) => boolean, expa
 /**
  * Expand all Objects and Arrays on a path
  */
-export function expandPath (data: JSONData, path: ?Path) : JSONData {
+export function expandPath (data: JSONData, path?: Path) : JSONData {
   let updatedData = data
 
   if (path) {
diff --git a/src/jsonPatchData.js b/src/jsonPatchData.js
index 9941d20..308d2fc 100644
--- a/src/jsonPatchData.js
+++ b/src/jsonPatchData.js
@@ -207,7 +207,7 @@ export function remove (data: JSONData, path: string) {
  * @param {JSONPatch} patch
  * @return {Array}
  */
-function simplifyPatch(patch: JSONPatch) {
+export function simplifyPatch(patch: JSONPatch) {
   const simplifiedPatch = []
   const paths = {}
 
diff --git a/src/types.js b/src/types.js
index 47f504a..c599c5d 100644
--- a/src/types.js
+++ b/src/types.js
@@ -39,7 +39,7 @@ export type PropertyData = {
   id: number,
   name: string,
   value: JSONData,
-  searchResult: ?SearchResultStatus
+  searchResult?: SearchResultStatus
 }
 
 export type ItemData = {
@@ -49,20 +49,20 @@ export type ItemData = {
 
 export type ObjectData = {
   type: 'Object',
-  expanded: ?boolean,
+  expanded?: boolean,
   props: PropertyData[]
 }
 
 export type ArrayData = {
   type: 'Array',
-  expanded: ?boolean,
+  expanded?: boolean,
   items: ItemData[]
 }
 
 export type ValueData = {
   type: 'value' | 'string',
-  value: ?any,
-  searchResult: ?SearchResultStatus
+  value?: any,
+  searchResult?: SearchResultStatus
 }
 
 export type JSONData = ObjectData | ArrayData | ValueData