diff --git a/aeson-helper.cabal b/aeson-helper.cabal
--- a/aeson-helper.cabal
+++ b/aeson-helper.cabal
@@ -1,5 +1,5 @@
 name:                aeson-helper
-version:             0.1.0.0
+version:             0.2.0.0
 synopsis:            Aeson helper func
 description:         Aeson helper func: replace union difference pick
 homepage:            https://github.com/Lupino/yuntan-common/tree/master/aeson-helper#readme
@@ -18,9 +18,8 @@
 
   exposed-modules:     Data.Aeson.Helper
   build-depends:       base >= 4.7 && < 5
-                     , unordered-containers
                      , text
-                     , aeson
+                     , aeson >= 2.0
                      , vector
   default-language:    Haskell2010
 
diff --git a/src/Data/Aeson/Helper.hs b/src/Data/Aeson/Helper.hs
--- a/src/Data/Aeson/Helper.hs
+++ b/src/Data/Aeson/Helper.hs
@@ -7,48 +7,82 @@
   , pick
   ) where
 
-import           Data.Aeson          (Value (..))
-import           Data.Maybe          (catMaybes)
-import           Data.Text           (Text)
-import qualified Data.Text           as T (isPrefixOf, stripPrefix)
-import qualified Data.Vector         as V (map)
-
-import           Data.HashMap.Strict (delete, insert, lookupDefault,
-                                      mapMaybeWithKey)
-import qualified Data.HashMap.Strict as HM (difference, union)
+import           Data.Aeson        (Value (..))
+import           Data.Aeson.Key    (Key, toText)
+import qualified Data.Aeson.KeyMap as KeyMap (delete, difference, insert,
+                                              lookup, mapMaybeWithKey, union)
+import           Data.Maybe        (catMaybes, fromMaybe)
+import           Data.Text         (Text)
+import qualified Data.Text         as T (isPrefixOf, stripPrefix)
+import qualified Data.Vector       as V (map)
 
-replace :: Text -> Text -> Value -> Value
-replace okey nkey (Object v) = Object . insert nkey ov $ delete okey v
-  where ov = lookupDefault Null okey v
+-- | Replace JSON key to a new key
+--
+-- >>> replace "okey" "nkey" (object [ "okey" := "value" ])
+-- Object (fromList [("nkey",String "value")])
+--
+-- >>> replace "okey" "nkey" (String "value")
+-- String "value"
+replace :: Key -> Key -> Value -> Value
+replace okey nkey (Object v) = Object . KeyMap.insert nkey ov $ KeyMap.delete okey v
+  where ov = fromMaybe Null $ KeyMap.lookup okey v
 
 replace _ _ v = v
 
+-- | Union two JSON
+--
+-- >>> union (object ["key1" .= "value1"]) (object ["key2" .= "value2"])
+-- Object (fromList [("key2",String "value2"),("key1",String "value1")])
+--
+-- >>> union (object ["key1" .= "value1"]) (object ["key1" .= "value2"])
+-- Object (fromList [("key1",String "value1")])
+--
+-- >>> union Null (object ["key2" .= "value2"])
+-- Object (fromList [("key2",String "value2")])
+--
+-- >>> union (object ["key1" .= "value1"]) Null
+-- Object (fromList [("key1",String "value1")])
 union :: Value -> Value -> Value
-union (Object a) (Object b) = Object $ HM.union a b
+union (Object a) (Object b) = Object $ KeyMap.union a b
 union (Object a) _          = Object a
 union _ (Object b)          = Object b
 union _ _                   = Null
 
+-- | Difference two JSON
+--
+-- >>> difference  (object ["key1" .= "value1", "key2" .= "value2"]) (object ["key1" .= Null])
+-- Object (fromList [("key2",String "value2")])
 difference :: Value -> Value -> Value
-difference (Object a) (Object b) = Object $ HM.difference a b
+difference (Object a) (Object b) = Object $ KeyMap.difference a b
 difference (Object a) _          = Object a
 difference _ _                   = Null
 
--- key1.key2.key3
+-- | Pick a value from JSON
+--
+-- >>> pick ["key1"] $ object ["key1" .= "value1", "key2" .= "value2", "key3" .= "value3"]
+-- Object (fromList [("key1",String "value1")])
+--
+-- >>> pick ["key1", "key2"] $ object ["key1" .= "value1", "key2" .= "value2", "key3" .= "value3"]
+-- Object (fromList [("key2",String "value2"),("key1",String "value1")])
+--
+-- >>> pick ["key3.key4"] $ object ["key1" .= "value1", "key2" .= "value2", "key3" .= object ["key4" .= "value4"]]
+-- Object (fromList [("key3",Object (fromList [("key4",String "value4")]))])
 pick :: [Text] -> Value -> Value
 pick [] v          = v
-pick ks (Object a) = Object $ mapMaybeWithKey (doMapMaybeWithKey ks) a
+pick ks (Object a) = Object $ KeyMap.mapMaybeWithKey (doMapMaybeWithKey ks) a
 pick ks (Array a)  = Array $ V.map (pick ks) a
 pick _ _           = Null
 
-doMapMaybeWithKey :: [Text] -> Text -> Value -> Maybe Value
-doMapMaybeWithKey ks k v = go ks
+doMapMaybeWithKey :: [Text] -> Key -> Value -> Maybe Value
+doMapMaybeWithKey ks key v = go ks
   where go :: [Text] -> Maybe Value
         go [] = Nothing
         go (x:xs)
           | k == x = Just v
           | (k <> "." ) `T.isPrefixOf` x = Just $ pick (catMaybes $ nextKeys ks k) v
           | otherwise = go xs
+
+        k = toText key
 
 nextKeys :: [Text] -> Text -> [Maybe Text]
 nextKeys [] _     = []