diff --git a/Libraries/Storage/AsyncStorage.js b/Libraries/Storage/AsyncStorage.js
index b8b6820276f6..4fc6ac6f0806 100644
--- a/Libraries/Storage/AsyncStorage.js
+++ b/Libraries/Storage/AsyncStorage.js
@@ -13,6 +13,8 @@
  */
 'use strict';
 
+import type { AsyncStorageBackend } from './AsyncStorageTypes';
+
 var NativeModules = require('NativeModules');
 var RCTAsyncSQLiteStorage = NativeModules.AsyncSQLiteDBStorage;
 var RCTAsyncRocksDBStorage = NativeModules.AsyncRocksDBStorage;
@@ -144,59 +146,6 @@ var AsyncStorage = {
     });
   },
 
-  /**
-   * 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.
-   *
-   * @param key Key of the item to modify.
-   * @param value New value to merge for the `key`.
-   * @param callback Function that will be called with any error.
-   * @returns A `Promise` object.
-   *
-   * @example <caption>Example</caption>
-   * 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'}}
-   */
-  mergeItem: function(
-    key: string,
-    value: string,
-    callback?: ?(error: ?Error) => void
-  ): Promise {
-    return new Promise((resolve, reject) => {
-      RCTAsyncStorage.multiMerge([[key,value]], function(errors) {
-        var errs = convertErrors(errors);
-        callback && callback(errs && errs[0]);
-        if (errs) {
-          reject(errs[0]);
-        } else {
-          resolve(null);
-        }
-      });
-    });
-  },
-
   /**
    * Erases *all* `AsyncStorage` for all clients, libraries, etc.  You probably
    * don't want to call this; use `removeItem` or `multiRemove` to clear only
@@ -406,86 +355,149 @@ var AsyncStorage = {
     });
   },
 
-  /**
-   * 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.
-   *
-   * @param keyValuePairs Array of key-value array for the items to merge.
-   * @param callback Function that will be called with an array of any
-   *    key-specific errors found.
-   * @returns A `Promise` object.
-   *
-   * @example <caption>Example</caption>
-   * // 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"}}
-   */
-  multiMerge: function(
-    keyValuePairs: Array<Array<string>>,
-    callback?: ?(errors: ?Array<Error>) => void
-  ): Promise {
-    return new Promise((resolve, reject) => {
-      RCTAsyncStorage.multiMerge(keyValuePairs, function(errors) {
-        var error = convertErrors(errors);
-        callback && callback(error);
-        if (error) {
-          reject(error);
-        } else {
-          resolve(null);
-        }
-      });
-    });
-  },
+  setBackend: function (
+    backend: AsyncStorageBackend
+  ) {
+    RCTAsyncStorage = backend;
+    // Not all native implementations support merge.
+    if (backend.multiMerge) {
+      AsyncStorage.mergeItem = mergeItem;
+      AsyncStorage.multiMerge = multiMerge;
+    } else {
+      delete AsyncStorage.mergeItem;
+      delete AsyncStorage.multiMerge;
+    }
+  }
 };
 
-// Not all native implementations support merge.
-if (!RCTAsyncStorage.multiMerge) {
-  delete AsyncStorage.mergeItem;
-  delete AsyncStorage.multiMerge;
+AsyncStorage.setBackend(RCTAsyncStorage);
+
+/**
+ * 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.
+ *
+ * @param keyValuePairs Array of key-value array for the items to merge.
+ * @param callback Function that will be called with an array of any
+ *    key-specific errors found.
+ * @returns A `Promise` object.
+ *
+ * @example <caption>Example</caption>
+ * // 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"}}
+ */
+function multiMerge (
+  keyValuePairs: Array<Array<string>>,
+  callback?: ?(errors: ?Array<Error>) => void
+): Promise {
+  return new Promise((resolve, reject) => {
+    RCTAsyncStorage.multiMerge(keyValuePairs, function(errors) {
+      var error = convertErrors(errors);
+      callback && callback(error);
+      if (error) {
+        reject(error);
+      } else {
+        resolve(null);
+      }
+    });
+  });
+}
+
+/**
+ * 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.
+ *
+ * @param key Key of the item to modify.
+ * @param value New value to merge for the `key`.
+ * @param callback Function that will be called with any error.
+ * @returns A `Promise` object.
+ *
+ * @example <caption>Example</caption>
+ * 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'}}
+ */
+function mergeItem(
+  key: string,
+  value: string,
+  callback?: ?(error: ?Error) => void
+): Promise {
+  return new Promise((resolve, reject) => {
+    RCTAsyncStorage.multiMerge([[key,value]], function(errors) {
+      var errs = convertErrors(errors);
+      callback && callback(errs && errs[0]);
+      if (errs) {
+        reject(errs[0]);
+      } else {
+        resolve(null);
+      }
+    });
+  });
 }
 
 function convertErrors(errs) {
diff --git a/Libraries/Storage/AsyncStorageTypes.js b/Libraries/Storage/AsyncStorageTypes.js
new file mode 100644
index 000000000000..7d1cb931c19b
--- /dev/null
+++ b/Libraries/Storage/AsyncStorageTypes.js
@@ -0,0 +1,13 @@
+/**
+ * @flow
+ */
+'use strict';
+
+export type AsyncStorageBackend = {
+  clear: Function,
+  getAllKeys: Function,
+  multiGet: Function,
+  multiSet: Function,
+  multiRemove: Function,
+  multiMerge?: Function
+};