Upstream dual-thread check from miso-lynx.

js/miso.js

@@ -238,6 +238,9 @@ function drill(c) {
       return c.child.domRef;
   }
 }
+function bts() {
+  return __BACKGROUND__;
+}
 
 // ts/miso/dom.ts
 function diff(c, n, parent, context) {
@@ -1108,6 +1111,7 @@ var drawingContext = {
 
 // ts/index.ts
 globalThis["miso"] = {
+  bts,
   hydrationContext,
   eventContext,
   drawingContext,

package.json

@@ -56,7 +56,7 @@
   },
   "homepage": "https://haskell-miso.org",
   "devDependencies": {
-    "@happy-dom/global-registrator": "^17.5.6",
+    "@happy-dom/global-registrator": "latest",
     "prettier": "3.5.3",
     "@types/bun": "latest"
   },

src/Miso.hs

@@ -4,6 +4,7 @@
 {-# LANGUAGE NamedFieldPuns            #-}
 {-# LANGUAGE RecordWildCards           #-}
 {-# LANGUAGE TemplateHaskell           #-}
+{-# LANGUAGE OverloadedStrings         #-}
 -----------------------------------------------------------------------------
 {-# OPTIONS_GHC -Wno-duplicate-exports #-}
 -----------------------------------------------------------------------------
@@ -201,5 +202,17 @@ withJS action = void $ do
 #ifdef WASM
   $(evalFile MISO_JS_PATH)
 #endif
+#ifdef GHCJS_NEW
+  FFI.consoleLog "withJS"
+  onBTS <- FFI.bts
+  if onBTS
+    then do
+      FFI.consoleLog "on bts"
+      void action
+    else do
+      FFI.consoleLog "on mts, bailing"
+      pure ()
+#else
   action
+#endif
 -----------------------------------------------------------------------------

src/Miso/FFI.hs

@@ -101,6 +101,8 @@ module Miso.FFI
   , splitmix32
     -- ** Math.random()
   , mathRandom
+    -- ** Native helpers
+  , bts
   ) where
 -----------------------------------------------------------------------------
 import           Miso.FFI.Internal

src/Miso/FFI/Internal.hs

@@ -148,6 +148,8 @@ module Miso.FFI.Internal
    , mathRandom
    -- * Crypto
    , getRandomValue
+   -- * Native
+   , bts
    ) where
 -----------------------------------------------------------------------------
 import           Control.Monad (void, forM_, (<=<), when)
@@ -460,14 +462,13 @@ diff (Object a) (Object b) c = do
 delegator :: JSVal -> JSVal -> Bool -> IO JSVal -> IO ()
 delegator mountPoint events debug getVTree = do
   ctx <- getEventContext
+  d <- toJSVal debug
 #ifdef WASM
   cb <- asyncCallback1 $ \continuation -> void (call continuation global =<< getVTree)
 #else
   cb <- syncCallback1 $ \continuation -> void (call continuation global =<< getVTree)
 #endif
-  d <- toJSVal debug
-  moduleMiso <- jsg "miso"
-  void $ moduleMiso # "delegator" $ [mountPoint,events,cb,d,ctx]
+  void $ ctx # "delegator" $ [mountPoint,events,cb,d,ctx]
 -----------------------------------------------------------------------------
 -- | Copies DOM pointers into virtual dom entry point into isomorphic javascript
 --
@@ -1037,3 +1038,6 @@ getRandomValue :: IO Double
 getRandomValue = fromJSValUnchecked =<< do
   jsg "miso" # "getRandomValues" $ ()
 -----------------------------------------------------------------------------
+bts :: IO Bool
+bts = fromJSValUnchecked =<< do jsg "miso" # "bts" $ ()
+-----------------------------------------------------------------------------

src/Miso/Runtime.hs

@@ -186,6 +186,7 @@ initialize events _componentParentId hydrate isRoot comp@Component {..} getCompo
         Diff.diff (Just oldVTree) (Just newVTree) _componentDOMRef
         FFI.updateRef oldVTree newVTree
         liftIO (atomicWriteIORef _componentVTree newVTree)
+        FFI.flush
 
   let _componentApplyActions = \(actions :: [action]) model_ comps -> do
         let info = ComponentInfo _componentId _componentParentId _componentDOMRef

ts/index.ts

@@ -22,6 +22,7 @@ import {
   getRandomValues,
   splitmix32,
   delegateEvent,
+  bts,
 } from './miso';
 
 import {
@@ -33,6 +34,7 @@ import {
 
 /* export globally */
 globalThis['miso'] = {
+    bts,
     hydrationContext,
     eventContext,
     drawingContext,

ts/miso.ts

@@ -18,6 +18,7 @@ import {
    updateRef,
    inline,
    typeOf,
+   bts,
    mathRandom,
    getRandomValues,
    splitmix32,
@@ -109,6 +110,7 @@ export {
   splitmix32,
   delegateEvent,
   getDOMRef,
+  bts,
 
   /* Types */
   VTree,

ts/miso/util.ts

@@ -298,3 +298,7 @@ export function drill<T>(c: VComp<T>): T {
       return c.child.domRef;
   }
 }
+
+export function bts () : boolean {
+  return __BACKGROUND__;
+}