[fix] AsyncStorage.mergeItem to support deep merge

Mirrors behaviour of react-native

src/apis/AsyncStorage/__tests__/index-test.js

@@ -1,5 +1,65 @@
 /* eslint-env mocha */
+import assert from 'assert';
+import AsyncStorage from '..';
+
+const waterfall = (fns, cb) => {
+  const _waterfall = (...args) => {
+    const fn = (fns || []).shift();
+    if (typeof fn === 'function') {
+      fn(...args, (err, ...nextArgs) => {
+        if (err) {
+          return cb(err);
+        } else {
+          return _waterfall(...nextArgs);
+        }
+      });
+    } else {
+      cb(null, ...args);
+    }
+  };
+  _waterfall();
+};
 
 suite('apis/AsyncStorage', () => {
-  test.skip('NO TEST COVERAGE', () => {});
+  suite('mergeLocalStorageItem', () => {
+    test('should have same behavior as react-native', (done) => {
+      // https://facebook.github.io/react-native/docs/asyncstorage.html
+      const UID123_object = {
+        name: 'Chris',
+        age: 30,
+        traits: { hair: 'brown', eyes: 'brown' }
+      };
+      const UID123_delta = {
+        age: 31,
+        traits: { eyes: 'blue', shoe_size: 10 }
+      };
+      waterfall([
+        (cb) => {
+          AsyncStorage.setItem('UID123', JSON.stringify(UID123_object))
+            .then(() => cb(null))
+            .catch(cb);
+        },
+        (cb) => {
+          AsyncStorage.mergeItem('UID123', JSON.stringify(UID123_delta))
+            .then(() => cb(null))
+            .catch(cb);
+        },
+        (cb) => {
+          AsyncStorage.getItem('UID123')
+            .then((result) => {
+              cb(null, JSON.parse(result));
+            })
+            .catch(cb);
+        }
+      ], (err, result) => {
+        assert.equal(err, null);
+        assert.deepEqual(result, {
+          'name': 'Chris', 'age': 31, 'traits': {
+            'shoe_size': 10, 'hair': 'brown', 'eyes': 'blue'
+          }
+        });
+        done();
+      });
+    });
+  });
 });

src/apis/AsyncStorage/index.js

@@ -3,12 +3,13 @@
  * Copyright (c) 2015-present, Facebook, Inc.
  * All rights reserved.
  */
+import merge from 'lodash/merge';
 
 const mergeLocalStorageItem = (key, value) => {
   const oldValue = window.localStorage.getItem(key);
   const oldObject = JSON.parse(oldValue);
   const newObject = JSON.parse(value);
-  const nextValue = JSON.stringify({ ...oldObject, ...newObject });
+  const nextValue = JSON.stringify(merge({}, oldObject, newObject));
   window.localStorage.setItem(key, nextValue);
 };