diff --git a/jsaddle.cabal b/jsaddle.cabal
--- a/jsaddle.cabal
+++ b/jsaddle.cabal
@@ -1,5 +1,5 @@
 name: jsaddle
-version: 0.9.0.0
+version: 0.9.2.0
 cabal-version: >=1.10
 build-type: Simple
 license: MIT
@@ -47,6 +47,8 @@
             stm >=2.4.4 && <2.5,
             time >=1.5.0.1 && <1.8,
             unordered-containers >=0.2 && <0.3,
+            uuid >=1.3.13 && <1.4,
+            uuid-types >=1.0.3 && <1.1,
             vector >=0.10 && <0.13
         exposed-modules:
             Data.JSString
@@ -81,8 +83,10 @@
             JavaScript.Array.Internal
             JavaScript.Object
             JavaScript.Object.Internal
+            Language.Javascript.JSaddle.Debug
             Language.Javascript.JSaddle.Native
             Language.Javascript.JSaddle.Native.Internal
+            Language.Javascript.JSaddle.Null
         hs-source-dirs: src-ghc
     exposed-modules:
         Language.Javascript.JSaddle
diff --git a/src/Language/Javascript/JSaddle/Debug.hs b/src/Language/Javascript/JSaddle/Debug.hs
new file mode 100644
--- /dev/null
+++ b/src/Language/Javascript/JSaddle/Debug.hs
@@ -0,0 +1,48 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+-----------------------------------------------------------------------------
+--
+-- Module      :  Language.Javascript.JSaddle.WebSockets
+-- Copyright   :  (c) Hamish Mackenzie
+-- License     :  MIT
+--
+-- Maintainer  :  Hamish Mackenzie <Hamish.K.Mackenzie@googlemail.com>
+--
+-- |
+--
+-----------------------------------------------------------------------------
+
+module Language.Javascript.JSaddle.Debug (
+    contexts
+  , addContext
+  , removeContext
+  , runOnAll
+  , runOnAll_
+) where
+
+import Language.Javascript.JSaddle
+       (runJSM, askJSM, JSM, JSContextRef(..))
+import Data.IORef (readIORef, atomicModifyIORef', newIORef, IORef)
+import System.IO.Unsafe (unsafePerformIO)
+import Data.Monoid ((<>))
+import Control.Monad.IO.Class (MonadIO(..))
+import Data.UUID (UUID)
+
+contexts :: IORef [JSContextRef]
+contexts = unsafePerformIO $ newIORef []
+{-# NOINLINE contexts #-}
+
+addContext :: JSM ()
+addContext = do
+    ctx <- askJSM
+    liftIO $ atomicModifyIORef' contexts $ \c -> (c <> [ctx], ())
+
+removeContext :: MonadIO m => UUID -> m ()
+removeContext uuid =
+    liftIO $ atomicModifyIORef' contexts $ \c -> (filter ((/= uuid) . contextId) c, ())
+
+runOnAll :: MonadIO m => JSM a -> m [a]
+runOnAll f = liftIO (readIORef contexts) >>= mapM (runJSM f)
+
+runOnAll_ :: MonadIO m => JSM a -> m ()
+runOnAll_ f = liftIO (readIORef contexts) >>= mapM_ (runJSM f)
diff --git a/src/Language/Javascript/JSaddle/Null.hs b/src/Language/Javascript/JSaddle/Null.hs
new file mode 100644
--- /dev/null
+++ b/src/Language/Javascript/JSaddle/Null.hs
@@ -0,0 +1,56 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+-----------------------------------------------------------------------------
+--
+-- Module      :  Language.Javascript.JSaddle.WebSockets
+-- Copyright   :  (c) Hamish Mackenzie
+-- License     :  MIT
+--
+-- Maintainer  :  Hamish Mackenzie <Hamish.K.Mackenzie@googlemail.com>
+--
+-- |
+--
+-----------------------------------------------------------------------------
+
+module Language.Javascript.JSaddle.Null (
+    run
+) where
+
+import Language.Javascript.JSaddle.Types
+       (BatchResults(..), JSM, JSStringReceived(..), Batch(..),
+        Results(..), Result(..), Command(..))
+import Control.Concurrent.Chan (readChan, writeChan, newChan)
+import Language.Javascript.JSaddle.Run (runJavaScript)
+import Control.Concurrent (forkIO)
+import Control.Monad (forever)
+import Data.Aeson (Value(..))
+import Data.Maybe (mapMaybe)
+
+-- | This is for performance testing JSaddle code that does not need to
+-- to read anything back from the JavaScript context.
+-- Anthing that does try to read will get JS null, 0 or "" back (depending
+-- on how the value is read).
+run :: JSM () -> IO ()
+run f = do
+    batches <- newChan
+    (processResult, _processSyncResult, start) <- runJavaScript (writeChan batches) f
+    _ <- forkIO $ forever $
+        readChan batches >>= \case
+            Batch commands _ batchNumber ->
+                processResult $ BatchResults batchNumber . Success $ mapMaybe (\case
+                        Left _ -> Nothing
+                        Right command -> Just $
+                            case command of
+                                DeRefVal _ -> DeRefValResult 0 ""
+                                ValueToBool _ -> ValueToBoolResult False
+                                ValueToNumber _ -> ValueToNumberResult 0
+                                ValueToString _ -> ValueToStringResult (JSStringReceived "")
+                                ValueToJSON _ -> ValueToJSONResult (JSStringReceived "null")
+                                ValueToJSONValue _ -> ValueToJSONValueResult Null
+                                IsNull _ -> IsNullResult True
+                                IsUndefined _ -> IsUndefinedResult False
+                                StrictEqual _ _ -> StrictEqualResult False
+                                InstanceOf _ _ -> InstanceOfResult False
+                                PropertyNames _ -> PropertyNamesResult []
+                                Sync -> SyncResult) commands
+    start
diff --git a/src/Language/Javascript/JSaddle/Run.hs b/src/Language/Javascript/JSaddle/Run.hs
--- a/src/Language/Javascript/JSaddle/Run.hs
+++ b/src/Language/Javascript/JSaddle/Run.hs
@@ -40,7 +40,7 @@
        (waitForAnimationFrame)
 #else
 import Control.Exception (throwIO)
-import Control.Monad (void, when, forever, zipWithM_)
+import Control.Monad (void, when, zipWithM_)
 import Control.Monad.IO.Class (MonadIO(..))
 import Control.Monad.Trans.Reader (ask, runReaderT)
 import Control.Monad.STM (atomically)
@@ -58,6 +58,7 @@
 import Data.Monoid ((<>))
 import qualified Data.Text as T (unpack)
 import qualified Data.Map as M (lookup, delete, insert, empty, size)
+import Data.UUID.V4 (nextRandom)
 import Data.Time.Clock (getCurrentTime,diffUTCTime)
 import Data.IORef (newIORef, atomicWriteIORef, readIORef)
 
@@ -68,8 +69,6 @@
 -- import Language.Javascript.JSaddle.Native.Internal (wrapJSVal)
 import Control.DeepSeq (deepseq)
 import GHC.Stats (getGCStatsEnabled, getGCStats, GCStats(..))
-import Data.Maybe (isJust)
-import Data.Foldable (forM_)
 #endif
 
 -- | Enable (or disable) JSaddle logging
@@ -151,6 +150,7 @@
 
 runJavaScript :: (Batch -> IO ()) -> JSM () -> IO (Results -> IO (), Results -> IO Batch, IO ())
 runJavaScript sendBatch entryPoint = do
+    contextId' <- nextRandom
     startTime' <- getCurrentTime
     recvMVar <- newEmptyMVar
     lastAsyncBatch <- newEmptyMVar
@@ -159,7 +159,8 @@
     nextRef' <- newTVarIO 0
     loggingEnabled <- newIORef False
     let ctx = JSContextRef {
-        startTime = startTime'
+        contextId = contextId'
+      , startTime = startTime'
       , doSendCommand = \cmd -> cmd `deepseq` do
             result <- newEmptyMVar
             atomically $ writeTChan commandChan (Right (cmd, result))
diff --git a/src/Language/Javascript/JSaddle/Types.hs b/src/Language/Javascript/JSaddle/Types.hs
--- a/src/Language/Javascript/JSaddle/Types.hs
+++ b/src/Language/Javascript/JSaddle/Types.hs
@@ -107,6 +107,7 @@
 import Control.Monad.Ref (MonadAtomicRef(..), MonadRef(..))
 import Control.Concurrent.STM.TVar (TVar)
 import Data.Text (Text)
+import Data.UUID (UUID)
 import Data.Time.Clock (UTCTime(..))
 import Data.Typeable (Typeable)
 import Data.Coerce (coerce, Coercible)
@@ -129,7 +130,8 @@
 type JSContextRef = ()
 #else
 data JSContextRef = JSContextRef {
-    startTime          :: UTCTime
+    contextId          :: UUID
+  , startTime          :: UTCTime
   , doSendCommand      :: Command -> IO Result
   , doSendAsyncCommand :: AsyncCommand -> IO ()
   , addCallback        :: Object -> JSCallAsFunction -> IO ()
@@ -211,19 +213,57 @@
     liftJSM' = id
     {-# INLINE liftJSM' #-}
 
-instance (MonadJSM m) => MonadJSM (ContT r m)
-instance (Error e, MonadJSM m) => MonadJSM (ErrorT e m)
-instance (MonadJSM m) => MonadJSM (ExceptT e m)
-instance (MonadJSM m) => MonadJSM (IdentityT m)
-instance (MonadJSM m) => MonadJSM (ListT m)
-instance (MonadJSM m) => MonadJSM (MaybeT m)
-instance (MonadJSM m) => MonadJSM (ReaderT r m)
-instance (Monoid w, MonadJSM m) => MonadJSM (Lazy.RWST r w s m)
-instance (Monoid w, MonadJSM m) => MonadJSM (Strict.RWST r w s m)
-instance (MonadJSM m) => MonadJSM (Lazy.StateT s m)
-instance (MonadJSM m) => MonadJSM (Strict.StateT s m)
-instance (Monoid w, MonadJSM m) => MonadJSM (Lazy.WriterT w m)
-instance (Monoid w, MonadJSM m) => MonadJSM (Strict.WriterT w m)
+instance (MonadJSM m) => MonadJSM (ContT r m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (Error e, MonadJSM m) => MonadJSM (ErrorT e m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (ExceptT e m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (IdentityT m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (ListT m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (MaybeT m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (ReaderT r m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (Monoid w, MonadJSM m) => MonadJSM (Lazy.RWST r w s m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (Monoid w, MonadJSM m) => MonadJSM (Strict.RWST r w s m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (Lazy.StateT s m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (MonadJSM m) => MonadJSM (Strict.StateT s m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (Monoid w, MonadJSM m) => MonadJSM (Lazy.WriterT w m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
+
+instance (Monoid w, MonadJSM m) => MonadJSM (Strict.WriterT w m) where
+    liftJSM' = lift . liftJSM'
+    {-# INLINE liftJSM' #-}
 
 instance MonadRef JSM where
     type Ref JSM = Ref IO