diff --git a/README.md b/README.md
index 80d0652..98b0ddd 100644
--- a/README.md
+++ b/README.md
@@ -108,6 +108,8 @@ import { recoilPersist } from 'recoil-persist'
 const { persistAtom } = recoilPersist({
   key: 'recoil-persist', // this key is using to store data in local storage
   storage: localStorage, // configurate which stroage will be used to store the data
+  stringify: JSON.stringify,
+  parser: JSON.parse,
 })
 ```
 
@@ -133,6 +135,23 @@ type config.storage = Storage
 Set `config.storage` with `sessionStorage` or other `Storage` implementation to
 change storage target. Otherwise `localStorage` is used (default).
 
+
+```js
+type config.stringify = Function
+```
+
+Set `config.stringify` with any method implementation to
+change the saved data. Otherwise `JSON.stringify` is used (default).
+
+
+```js
+type config.parser = Function
+```
+
+Set `config.parser` with any method implementation to
+change/transfer return data. Otherwise `JSON.parse` is used (default).
+
+
 ## Migration from version 1.x.x to 2.x.x
 
 The API changed from version 1.x.x.
@@ -154,7 +173,7 @@ const {
 -   ['count'], // no need for specifying atoms keys
     {
         key: 'recoil-persist', // configuration stay the same too
-        storage: localStorage
+        storage: localStorage,
     }
 )
 
diff --git a/src/index.ts b/src/index.ts
index 45d1871..89737e6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -9,6 +9,8 @@ export interface PersistStorage {
 export interface PersistConfiguration {
   key?: string
   storage?: PersistStorage
+  stringify?: (value: any) => any
+  parser?: (value: any) => any
 }
 
 /**
@@ -27,27 +29,34 @@ export const recoilPersist = (
     }
   }
 
-  const { key = 'recoil-persist', storage = localStorage } = config
-
+  const {
+    key = 'recoil-persist',
+    storage = localStorage,
+    stringify = JSON.stringify,
+    parser = JSON.parse,
+  } = config
   const persistAtom: AtomEffect<any> = ({ onSet, node, trigger, setSelf }) => {
     if (trigger === 'get') {
       const state = getState()
       if (typeof state.then === 'function') {
-        state.then((s) => {
-          if (s.hasOwnProperty(node.key)) {
+        state.then((s: any) => {
+          if (s && s.hasOwnProperty(node.key)) {
             setSelf(s[node.key])
           }
         })
       }
+
       if (state.hasOwnProperty(node.key)) {
         setSelf(state[node.key])
       }
     }
 
-    onSet(async (newValue, _, isReset) => {
+    onSet((newValue, _, isReset) => {
       const state = getState()
       if (typeof state.then === 'function') {
-        state.then((s: any) => updateState(newValue, s, node.key, isReset))
+        state.then((s: any) =>
+          updateState(newValue, s ?? {}, node.key, isReset),
+        )
       } else {
         updateState(newValue, state, node.key, isReset)
       }
@@ -89,7 +98,7 @@ export const recoilPersist = (
       return {}
     }
     try {
-      return JSON.parse(state)
+      return parser(state)
     } catch (e) {
       console.error(e)
       return {}
@@ -99,9 +108,9 @@ export const recoilPersist = (
   const setState = (state: any): void => {
     try {
       if (typeof storage.mergeItem === 'function') {
-        storage.mergeItem(key, JSON.stringify(state))
+        storage.mergeItem(key, stringify(state))
       } else {
-        storage.setItem(key, JSON.stringify(state))
+        storage.setItem(key, stringify(state))
       }
     } catch (e) {
       console.error(e)