react-native/docs/asyncstorage.md

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AsyncStorage is a simple, unencrypted, asynchronous, persistent, key-value storage system that is global to the app. It should be used instead of LocalStorage.

It is recommended that you use an abstraction on top of AsyncStorage instead of AsyncStorage directly for anything more than light usage since it operates globally.

On iOS, AsyncStorage is backed by native code that stores small values in a serialized dictionary and larger values in separate files. On Android, AsyncStorage will use either RocksDB or SQLite based on what is available.

The AsyncStorage JavaScript code is a simple facade that provides a clear JavaScript API, real Error objects, and simple non-multi functions. Each method in the API returns a Promise object.

Persisting data:

try {
  await AsyncStorage.setItem('@MySuperStore:key', 'I like to save it.');
} catch (error) {
  // Error saving data
}

Fetching data:

try {
  const value = await AsyncStorage.getItem('@MySuperStore:key');
  if (value !== null){
    // We have data!!
    console.log(value);
  }
} catch (error) {
  // Error retrieving data
}

Methods

• getItem
• setItem
• removeItem
• mergeItem
• clear
• getAllKeys
• flushGetRequests
• multiGet
• multiSet
• multiRemove
• multiMerge

---

Reference

Methods

getItem()

static getItem(key: string, [callback]: ?(error: ?Error, result: ?string) => void)

Fetches an item for a key and invokes a callback upon completion. Returns a Promise object.

Parameters:

Name	Type	Required	Description
key	string	No	Key of the item to fetch.
callback	?(error: ?Error, result: ?string) => void	Yes	Function that will be called with a result if found or any error.

---

setItem()

static setItem(key: string, value: string, [callback]: ?(error: ?Error) => void)

Sets the value for a key and invokes a callback upon completion. Returns a Promise object.

Parameters:

Name	Type	Required	Description
key	string	No	Key of the item to set.
value	string	No	Value to set for the key.
callback	?(error: ?Error) => void	Yes	Function that will be called with any error.

---

removeItem()

static removeItem(key: string, [callback]: ?(error: ?Error) => void)

Removes an item for a key and invokes a callback upon completion. Returns a Promise object.

Parameters:

Name	Type	Required	Description
key	string	No	Key of the item to remove.
callback	?(error: ?Error) => void	Yes	Function that will be called with any error.

---

mergeItem()

static mergeItem(key: string, value: string, [callback]: ?(error: ?Error) => void)

Merges an existing key value with an input value, assuming both values are stringified JSON. Returns a Promise object.

NOTE: This is not supported by all native implementations.

Parameters:

Name	Type	Required	Description
key	string	No	Key of the item to modify.
value	string	No	New value to merge for the key.
callback	?(error: ?Error) => void	Yes	Function that will be called with any error.

Example:

let UID123_object = {
 name: 'Chris',
 age: 30,
 traits: {hair: 'brown', eyes: 'brown'},
};
// You only need to define what will be added or updated
let UID123_delta = {
 age: 31,
 traits: {eyes: 'blue', shoe_size: 10}
};

AsyncStorage.setItem('UID123', JSON.stringify(UID123_object), () => {
  AsyncStorage.mergeItem('UID123', JSON.stringify(UID123_delta), () => {
    AsyncStorage.getItem('UID123', (err, result) => {
      console.log(result);
    });
  });
});

// Console log result:
// => {'name':'Chris','age':31,'traits':
//    {'shoe_size':10,'hair':'brown','eyes':'blue'}}

---

clear()

static clear([callback]: ?(error: ?Error) => void)

Erases all AsyncStorage for all clients, libraries, etc. You probably don't want to call this; use removeItem or multiRemove to clear only your app's keys. Returns a Promise object.

Parameters:

Name	Type	Required	Description
callback	?(error: ?Error) => void	Yes	Function that will be called with any error.

---

getAllKeys()

static getAllKeys([callback]: ?(error: ?Error, keys: ?Array<string>) => void)

Gets all keys known to your app; for all callers, libraries, etc. Returns a Promise object.

Parameters:

Name	Type	Required	Description
callback	?(error: ?Error, keys: ?Array) => void	Yes	Function that will be called the keys found and any error.

---

flushGetRequests()

static flushGetRequests(): [object Object]

Flushes any pending requests using a single batch call to get the data.

---

multiGet()

static multiGet(keys: Array<string>, [callback]: ?(errors: ?Array<Error>, result: ?Array<Array<string>>) => void)

This allows you to batch the fetching of items given an array of key inputs. Your callback will be invoked with an array of corresponding key-value pairs found:

multiGet(['k1', 'k2'], cb) -> cb([['k1', 'val1'], ['k2', 'val2']])

The method returns a Promise object.

Parameters:

Name	Type	Required	Description
keys	Array	No	Array of key for the items to get.
callback	?(errors: ?Array, result: ?Array<Array>) => void	Yes	Function that will be called with a key-value array of the results, plus an array of any key-specific errors found.

Example:

AsyncStorage.getAllKeys((err, keys) => {
  AsyncStorage.multiGet(keys, (err, stores) => {
   stores.map((result, i, store) => {
     // get at each store's key/value so you can work with it
     let key = store[i][0];
     let value = store[i][1];
    });
  });
});

---

multiSet()

static multiSet(keyValuePairs: Array<Array<string>>, [callback]: ?(errors: ?Array<Error>) => void)

Use this as a batch operation for storing multiple key-value pairs. When the operation completes you'll get a single callback with any errors:

multiSet([['k1', 'val1'], ['k2', 'val2']], cb);

The method returns a Promise object.

Parameters:

Name	Type	Required	Description
keyValuePairs	Array<Array>	No	Array of key-value array for the items to set.
callback	?(errors: ?Array) => void	Yes	Function that will be called with an array of any key-specific errors found.

---

multiRemove()

static multiRemove(keys: Array<string>, [callback]: ?(errors: ?Array<Error>) => void)

Call this to batch the deletion of all keys in the keys array. Returns a Promise object.

Parameters:

Name	Type	Required	Description
keys	Array	No	Array of key for the items to delete.
callback	?(errors: ?Array) => void	Yes	Function that will be called an array of any key-specific errors found.

Example:

let keys = ['k1', 'k2'];
AsyncStorage.multiRemove(keys, (err) => {
  // keys k1 & k2 removed, if they existed
  // do most stuff after removal (if you want)
});

---

multiMerge()

static multiMerge(keyValuePairs: Array<Array<string>>, [callback]: ?(errors: ?Array<Error>) => void)

Batch operation to merge in existing and new values for a given set of keys. This assumes that the values are stringified JSON. Returns a Promise object.

NOTE: This is not supported by all native implementations.

Parameters:

Name	Type	Required	Description
keyValuePairs	Array<Array>	No	Array of key-value array for the items to merge.
callback	?(errors: ?Array) => void	Yes	Function that will be called with an array of any key-specific errors found.

Example:

// first user, initial values
let UID234_object = {
 name: 'Chris',
 age: 30,
 traits: {hair: 'brown', eyes: 'brown'},
};

// first user, delta values
let UID234_delta = {
 age: 31,
 traits: {eyes: 'blue', shoe_size: 10},
};

// second user, initial values
let UID345_object = {
 name: 'Marge',
 age: 25,
 traits: {hair: 'blonde', eyes: 'blue'},
};

// second user, delta values
let UID345_delta = {
 age: 26,
 traits: {eyes: 'green', shoe_size: 6},
};

let multi_set_pairs   = [['UID234', JSON.stringify(UID234_object)], ['UID345', JSON.stringify(UID345_object)]]
let multi_merge_pairs = [['UID234', JSON.stringify(UID234_delta)], ['UID345', JSON.stringify(UID345_delta)]]

AsyncStorage.multiSet(multi_set_pairs, (err) => {
  AsyncStorage.multiMerge(multi_merge_pairs, (err) => {
    AsyncStorage.multiGet(['UID234','UID345'], (err, stores) => {
      stores.map( (result, i, store) => {
        let key = store[i][0];
        let val = store[i][1];
        console.log(key, val);
      });
    });
  });
});

// Console log results:
// => UID234 {"name":"Chris","age":31,"traits":{"shoe_size":10,"hair":"brown","eyes":"blue"}}
// => UID345 {"name":"Marge","age":26,"traits":{"shoe_size":6,"hair":"blonde","eyes":"green"}}