diff --git a/fpdfsdk/javascript/Consts.cpp b/fpdfsdk/javascript/Consts.cpp
index b71d0a3..19988a6 100644
--- a/fpdfsdk/javascript/Consts.cpp
+++ b/fpdfsdk/javascript/Consts.cpp
@@ -148,7 +148,7 @@
         (rt)->GetIsolate(), (name),                                        \
         [](const v8::FunctionCallbackInfo<v8::Value>& info) {              \
           CJS_Runtime* pLocalRuntime = static_cast<CJS_Runtime*>(          \
-              FXJS_GetRuntimeFromIsolate(info.GetIsolate()));              \
+              FXJS_GetCurrentEngineFromIsolate(info.GetIsolate()));        \
           if (pLocalRuntime)                                               \
             info.GetReturnValue().Set(pLocalRuntime->GetConstArray(name)); \
         });                                                                \
diff --git a/fpdfsdk/javascript/JS_Define.h b/fpdfsdk/javascript/JS_Define.h
index 4c24a4d..b9ae140 100644
--- a/fpdfsdk/javascript/JS_Define.h
+++ b/fpdfsdk/javascript/JS_Define.h
@@ -78,7 +78,7 @@
                   const v8::PropertyCallbackInfo<v8::Value>& info) {
   v8::Isolate* isolate = info.GetIsolate();
   CJS_Runtime* pRuntime =
-      static_cast<CJS_Runtime*>(FXJS_GetRuntimeFromIsolate(isolate));
+      static_cast<CJS_Runtime*>(FXJS_GetCurrentEngineFromIsolate(isolate));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
@@ -104,7 +104,7 @@
                   const v8::PropertyCallbackInfo<void>& info) {
   v8::Isolate* isolate = info.GetIsolate();
   CJS_Runtime* pRuntime =
-      static_cast<CJS_Runtime*>(FXJS_GetRuntimeFromIsolate(isolate));
+      static_cast<CJS_Runtime*>(FXJS_GetCurrentEngineFromIsolate(isolate));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
@@ -143,7 +143,7 @@
               const v8::FunctionCallbackInfo<v8::Value>& info) {
   v8::Isolate* isolate = info.GetIsolate();
   CJS_Runtime* pRuntime =
-      static_cast<CJS_Runtime*>(FXJS_GetRuntimeFromIsolate(isolate));
+      static_cast<CJS_Runtime*>(FXJS_GetCurrentEngineFromIsolate(isolate));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
@@ -245,7 +245,7 @@
   }
 
 #define DECLARE_JS_CLASS_RICH_PART()                                           \
-  static void JSConstructor(IJS_Runtime* pRuntime, v8::Local<v8::Object> obj); \
+  static void JSConstructor(CFXJS_Engine* pEngine, v8::Local<v8::Object> obj); \
   static void JSDestructor(v8::Local<v8::Object> obj);                         \
   static void DefineProps(v8::Isolate* pIsoalte);                              \
   static void DefineMethods(v8::Isolate* pIsoalte);                            \
@@ -254,12 +254,12 @@
 
 #define IMPLEMENT_JS_CLASS_RICH_PART(js_class_name, class_alternate,          \
                                      class_name)                              \
-  void js_class_name::JSConstructor(IJS_Runtime* pIRuntime,                   \
+  void js_class_name::JSConstructor(CFXJS_Engine* pEngine,                    \
                                     v8::Local<v8::Object> obj) {              \
     CJS_Object* pObj = new js_class_name(obj);                                \
     pObj->SetEmbedObject(new class_alternate(pObj));                          \
     FXJS_SetPrivate(nullptr, obj, (void*)pObj);                               \
-    pObj->InitInstance(pIRuntime);                                            \
+    pObj->InitInstance(static_cast<CJS_Runtime*>(pEngine));                   \
   }                                                                           \
   void js_class_name::JSDestructor(v8::Local<v8::Object> obj) {               \
     js_class_name* pObj = (js_class_name*)FXJS_GetPrivate(nullptr, obj);      \
@@ -366,7 +366,7 @@
                       const v8::PropertyCallbackInfo<v8::Value>& info) {
   v8::Isolate* isolate = info.GetIsolate();
   CJS_Runtime* pRuntime =
-      static_cast<CJS_Runtime*>(FXJS_GetRuntimeFromIsolate(isolate));
+      static_cast<CJS_Runtime*>(FXJS_GetCurrentEngineFromIsolate(isolate));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
@@ -393,7 +393,7 @@
                       const v8::PropertyCallbackInfo<v8::Value>& info) {
   v8::Isolate* isolate = info.GetIsolate();
   CJS_Runtime* pRuntime =
-      static_cast<CJS_Runtime*>(FXJS_GetRuntimeFromIsolate(isolate));
+      static_cast<CJS_Runtime*>(FXJS_GetCurrentEngineFromIsolate(isolate));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
@@ -416,7 +416,8 @@
                       v8::Local<v8::String> property,
                       const v8::PropertyCallbackInfo<v8::Boolean>& info) {
   v8::Isolate* isolate = info.GetIsolate();
-  IJS_Runtime* pRuntime = FXJS_GetRuntimeFromIsolate(isolate);
+  CJS_Runtime* pRuntime =
+      static_cast<CJS_Runtime*>(FXJS_GetCurrentEngineFromIsolate(isolate));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
@@ -440,8 +441,8 @@
                        CFX_WideString&)>
 void JSGlobalFunc(const char* func_name_string,
                   const v8::FunctionCallbackInfo<v8::Value>& info) {
-  CJS_Runtime* pRuntime =
-      static_cast<CJS_Runtime*>(FXJS_GetRuntimeFromIsolate(info.GetIsolate()));
+  CJS_Runtime* pRuntime = static_cast<CJS_Runtime*>(
+      FXJS_GetCurrentEngineFromIsolate(info.GetIsolate()));
   if (!pRuntime)
     return;
   IJS_Context* pContext = pRuntime->GetCurrentContext();
diff --git a/fpdfsdk/javascript/cjs_runtime.cpp b/fpdfsdk/javascript/cjs_runtime.cpp
index 7eaf145..36d888a 100644
--- a/fpdfsdk/javascript/cjs_runtime.cpp
+++ b/fpdfsdk/javascript/cjs_runtime.cpp
@@ -58,8 +58,7 @@
 CJS_Runtime::CJS_Runtime(CPDFDoc_Environment* pApp)
     : m_pApp(pApp),
       m_pDocument(nullptr),
-      m_bBlocking(FALSE),
-      m_isolate(nullptr),
+      m_bBlocking(false),
       m_isolateManaged(false) {
 #ifndef PDF_ENABLE_XFA
   IPDF_JSPLATFORM* pPlatform = m_pApp->GetFormFillInfo()->m_pJsPlatform;
@@ -96,7 +95,7 @@
   v8::HandleScope handle_scope(isolate);
   if (CPDFXFA_App::GetInstance()->IsJavaScriptInitialized()) {
     CJS_Context* pContext = (CJS_Context*)NewContext();
-    FXJS_InitializeRuntime(GetIsolate(), this, &m_context, &m_StaticObjects);
+    FXJS_InitializeEngine(GetIsolate(), this, &m_context, &m_StaticObjects);
     ReleaseContext(pContext);
     return;
   }
@@ -110,7 +109,7 @@
 #endif
 
   CJS_Context* pContext = (CJS_Context*)NewContext();
-  FXJS_InitializeRuntime(GetIsolate(), this, &m_context, &m_StaticObjects);
+  FXJS_InitializeEngine(GetIsolate(), this, &m_context, &m_StaticObjects);
   ReleaseContext(pContext);
 }
 
@@ -120,7 +119,7 @@
 
   m_ContextArray.clear();
   m_ConstArrays.clear();
-  FXJS_ReleaseRuntime(GetIsolate(), &m_context, &m_StaticObjects);
+  FXJS_ReleaseEngine(GetIsolate(), &m_context, &m_StaticObjects);
   m_context.Reset();
   if (m_isolateManaged)
     m_isolate->Dispose();
@@ -284,7 +283,7 @@
   // Do so now.
   // TODO(tsepez): redesign PDF-side objects to not rely on v8::Context's
   // embedder data slots, and/or to always use the right context.
-  FXJS_SetRuntimeForV8Context(old_context, this);
+  FXJS_SetEngineForV8Context(old_context, this);
 
   v8::Local<v8::Value> propvalue =
       context->Global()->Get(v8::String::NewFromUtf8(
diff --git a/fpdfsdk/javascript/cjs_runtime.h b/fpdfsdk/javascript/cjs_runtime.h
index c43a34b..16432d5 100644
--- a/fpdfsdk/javascript/cjs_runtime.h
+++ b/fpdfsdk/javascript/cjs_runtime.h
@@ -20,7 +20,7 @@
 
 class CJS_Context;
 
-class CJS_Runtime : public IJS_Runtime {
+class CJS_Runtime : public IJS_Runtime, public CFXJS_Engine {
  public:
   class Observer {
    public:
@@ -77,13 +77,9 @@
   std::vector<std::unique_ptr<CJS_Context>> m_ContextArray;
   CPDFDoc_Environment* const m_pApp;
   CPDFSDK_Document* m_pDocument;
-  FX_BOOL m_bBlocking;
-  std::set<FieldEvent> m_FieldEventSet;
-  v8::Isolate* m_isolate;
+  bool m_bBlocking;
   bool m_isolateManaged;
-  v8::Global<v8::Context> m_context;
-  std::vector<v8::Global<v8::Object>*> m_StaticObjects;
-  std::map<CFX_WideString, v8::Global<v8::Array>> m_ConstArrays;
+  std::set<FieldEvent> m_FieldEventSet;
   std::set<Observer*> m_observers;
 };
 
diff --git a/fxjs/fxjs_v8.cpp b/fxjs/fxjs_v8.cpp
index 92207fd..42fc021 100644
--- a/fxjs/fxjs_v8.cpp
+++ b/fxjs/fxjs_v8.cpp
@@ -222,6 +222,9 @@
     : m_pFXJSERuntimeData(nullptr), m_pDynamicObjsMap(nullptr) {}
 #endif  // PDF_ENABLE_XFA
 
+CFXJS_Engine::CFXJS_Engine() : m_isolate(nullptr) {}
+CFXJS_Engine::~CFXJS_Engine() {}
+
 int FXJS_DefineObj(v8::Isolate* pIsolate,
                    const wchar_t* sObjName,
                    FXJSOBJTYPE eObjType,
@@ -330,9 +333,9 @@
       fun);
 }
 
-void FXJS_InitializeRuntime(
+void FXJS_InitializeEngine(
     v8::Isolate* pIsolate,
-    IJS_Runtime* pIRuntime,
+    CFXJS_Engine* pEngine,
     v8::Global<v8::Context>* pV8PersistentContext,
     std::vector<v8::Global<v8::Object>*>* pStaticObjects) {
   if (pIsolate == g_isolate)
@@ -353,7 +356,7 @@
   if (!pData)
     return;
   pData->CreateDynamicObjsMap(pIsolate);
-  v8Context->SetAlignedPointerInEmbedderData(kPerContextDataIndex, pIRuntime);
+  v8Context->SetAlignedPointerInEmbedderData(kPerContextDataIndex, pEngine);
 
   int maxID = CFXJS_ObjDefinition::MaxID(pIsolate);
   pStaticObjects->resize(maxID + 1);
@@ -367,10 +370,10 @@
           ->SetAlignedPointerInInternalField(0, new CFXJS_PerObjectData(i));
 
       if (pObjDef->m_pConstructor)
-        pObjDef->m_pConstructor(pIRuntime, v8Context->Global()
-                                               ->GetPrototype()
-                                               ->ToObject(v8Context)
-                                               .ToLocalChecked());
+        pObjDef->m_pConstructor(pEngine, v8Context->Global()
+                                             ->GetPrototype()
+                                             ->ToObject(v8Context)
+                                             .ToLocalChecked());
     } else if (pObjDef->m_ObjType == FXJSOBJTYPE_STATIC) {
       CFX_ByteString bs = CFX_WideString(pObjDef->m_ObjName).UTF8Encode();
       v8::Local<v8::String> m_ObjName =
@@ -379,7 +382,7 @@
               .ToLocalChecked();
 
       v8::Local<v8::Object> obj =
-          FXJS_NewFxDynamicObj(pIsolate, pIRuntime, i, true);
+          FXJS_NewFxDynamicObj(pIsolate, pEngine, i, true);
       v8Context->Global()->Set(v8Context, m_ObjName, obj).FromJust();
       pStaticObjects->at(i) = new v8::Global<v8::Object>(pIsolate, obj);
     }
@@ -387,9 +390,9 @@
   pV8PersistentContext->Reset(pIsolate, v8Context);
 }
 
-void FXJS_ReleaseRuntime(v8::Isolate* pIsolate,
-                         v8::Global<v8::Context>* pV8PersistentContext,
-                         std::vector<v8::Global<v8::Object>*>* pStaticObjects) {
+void FXJS_ReleaseEngine(v8::Isolate* pIsolate,
+                        v8::Global<v8::Context>* pV8PersistentContext,
+                        std::vector<v8::Global<v8::Object>*>* pStaticObjects) {
   v8::Isolate::Scope isolate_scope(pIsolate);
   v8::HandleScope handle_scope(pIsolate);
   v8::Local<v8::Context> context =
@@ -431,16 +434,16 @@
   delete pData;
 }
 
-IJS_Runtime* FXJS_GetRuntimeFromIsolate(v8::Isolate* pIsolate) {
+CFXJS_Engine* FXJS_GetCurrentEngineFromIsolate(v8::Isolate* pIsolate) {
   v8::Local<v8::Context> context = pIsolate->GetCurrentContext();
-  return static_cast<IJS_Runtime*>(
+  return static_cast<CFXJS_Engine*>(
       context->GetAlignedPointerFromEmbedderData(kPerContextDataIndex));
 }
 
 #ifdef PDF_ENABLE_XFA
-void FXJS_SetRuntimeForV8Context(v8::Local<v8::Context> v8Context,
-                                 IJS_Runtime* pIRuntime) {
-  v8Context->SetAlignedPointerInEmbedderData(kPerContextDataIndex, pIRuntime);
+void FXJS_SetEngineForV8Context(v8::Local<v8::Context> v8Context,
+                                CFXJS_Engine* pEngine) {
+  v8Context->SetAlignedPointerInEmbedderData(kPerContextDataIndex, pEngine);
 }
 #endif  // PDF_ENABLE_XFA
 
@@ -473,7 +476,7 @@
 }
 
 v8::Local<v8::Object> FXJS_NewFxDynamicObj(v8::Isolate* pIsolate,
-                                           IJS_Runtime* pIRuntime,
+                                           CFXJS_Engine* pEngine,
                                            int nObjDefnID,
                                            bool bStatic) {
   v8::Isolate::Scope isolate_scope(pIsolate);
@@ -502,7 +505,7 @@
   CFXJS_PerObjectData* pPerObjData = new CFXJS_PerObjectData(nObjDefnID);
   obj->SetAlignedPointerInInternalField(0, pPerObjData);
   if (pObjDef->m_pConstructor)
-    pObjDef->m_pConstructor(pIRuntime, obj);
+    pObjDef->m_pConstructor(pEngine, obj);
 
   if (!bStatic && FXJS_PerIsolateData::Get(pIsolate)->m_pDynamicObjsMap) {
     FXJS_PerIsolateData::Get(pIsolate)->m_pDynamicObjsMap->set(pPerObjData,
diff --git a/fxjs/fxjs_v8_embeddertest.cpp b/fxjs/fxjs_v8_embeddertest.cpp
index 71b004c..b573939 100644
--- a/fxjs/fxjs_v8_embeddertest.cpp
+++ b/fxjs/fxjs_v8_embeddertest.cpp
@@ -44,19 +44,17 @@
   CheckAssignmentInCurrentContext(kExpected1);
 }
 
-TEST_F(FXJSV8EmbedderTest, MultipleRutimes) {
+TEST_F(FXJSV8EmbedderTest, MultipleEngines) {
   v8::Isolate::Scope isolate_scope(isolate());
   v8::HandleScope handle_scope(isolate());
 
   v8::Global<v8::Context> global_context1;
   std::vector<v8::Global<v8::Object>*> static_objects1;
-  FXJS_InitializeRuntime(isolate(), nullptr, &global_context1,
-                         &static_objects1);
+  FXJS_InitializeEngine(isolate(), nullptr, &global_context1, &static_objects1);
 
   v8::Global<v8::Context> global_context2;
   std::vector<v8::Global<v8::Object>*> static_objects2;
-  FXJS_InitializeRuntime(isolate(), nullptr, &global_context2,
-                         &static_objects2);
+  FXJS_InitializeEngine(isolate(), nullptr, &global_context2, &static_objects2);
 
   v8::Context::Scope context_scope(GetV8Context());
   ExecuteInCurrentContext(CFX_WideString(kScript0));
@@ -69,7 +67,7 @@
     ExecuteInCurrentContext(CFX_WideString(kScript1));
     CheckAssignmentInCurrentContext(kExpected1);
   }
-  FXJS_ReleaseRuntime(isolate(), &global_context1, &static_objects1);
+  FXJS_ReleaseEngine(isolate(), &global_context1, &static_objects1);
 
   {
     v8::Local<v8::Context> context2 =
@@ -78,7 +76,7 @@
     ExecuteInCurrentContext(CFX_WideString(kScript2));
     CheckAssignmentInCurrentContext(kExpected2);
   }
-  FXJS_ReleaseRuntime(isolate(), &global_context2, &static_objects2);
+  FXJS_ReleaseEngine(isolate(), &global_context2, &static_objects2);
 
   CheckAssignmentInCurrentContext(kExpected0);
 }
diff --git a/fxjs/include/fxjs_v8.h b/fxjs/include/fxjs_v8.h
index 5e12b08..52afc49 100644
--- a/fxjs/include/fxjs_v8.h
+++ b/fxjs/include/fxjs_v8.h
@@ -17,16 +17,17 @@
 #include <v8-util.h>
 #include <v8.h>
 
+#include <map>
 #include <vector>
 
 #include "core/fxcrt/include/fx_string.h"
 
+class CFXJS_Engine;
 class CFXJS_ObjDefinition;
 
-// FXJS_V8 places no restrictions on these two classes; it merely passes them
+// FXJS_V8 places no restrictions on this class; it merely passes it
 // on to caller-provided methods.
 class IJS_Context;  // A description of the event that caused JS execution.
-class IJS_Runtime;  // A native runtime, typically owns the v8::Context.
 
 #ifdef PDF_ENABLE_XFA
 // FXJS_V8 places no interpreation on this calass; it merely passes it
@@ -124,12 +125,25 @@
   void Free(void* data, size_t length) override;
 };
 
-using FXJS_CONSTRUCTOR = void (*)(IJS_Runtime* cc, v8::Local<v8::Object> obj);
+using FXJS_CONSTRUCTOR = void (*)(CFXJS_Engine* fxjs,
+                                  v8::Local<v8::Object> obj);
 using FXJS_DESTRUCTOR = void (*)(v8::Local<v8::Object> obj);
 
 void FXJS_Initialize(unsigned int embedderDataSlot, v8::Isolate* pIsolate);
 void FXJS_Release();
 
+class CFXJS_Engine {
+ public:
+  CFXJS_Engine();
+  ~CFXJS_Engine();
+
+ protected:
+  v8::Isolate* m_isolate;
+  v8::Global<v8::Context> m_context;
+  std::vector<v8::Global<v8::Object>*> m_StaticObjects;
+  std::map<CFX_WideString, v8::Global<v8::Array>> m_ConstArrays;
+};
+
 // Gets the global isolate set by FXJS_Initialize(), or makes a new one each
 // time if there is no such isolate. Returns true if a new isolate had to be
 // created.
@@ -172,30 +186,30 @@
                             v8::FunctionCallback pConstGetter);
 
 // Called after FXJS_Define* calls made.
-void FXJS_InitializeRuntime(
+void FXJS_InitializeEngine(
     v8::Isolate* pIsolate,
-    IJS_Runtime* pIRuntime,
+    CFXJS_Engine* pEngine,
     v8::Global<v8::Context>* pV8PersistentContext,
     std::vector<v8::Global<v8::Object>*>* pStaticObjects);
-void FXJS_ReleaseRuntime(v8::Isolate* pIsolate,
-                         v8::Global<v8::Context>* pV8PersistentContext,
-                         std::vector<v8::Global<v8::Object>*>* pStaticObjects);
-IJS_Runtime* FXJS_GetRuntimeFromIsolate(v8::Isolate* pIsolate);
+void FXJS_ReleaseEngine(v8::Isolate* pIsolate,
+                        v8::Global<v8::Context>* pV8PersistentContext,
+                        std::vector<v8::Global<v8::Object>*>* pStaticObjects);
+CFXJS_Engine* FXJS_GetCurrentEngineFromIsolate(v8::Isolate* pIsolate);
 
 #ifdef PDF_ENABLE_XFA
-// Called as part of FXJS_InitializeRuntime, exposed so PDF can make its
+// Called as part of FXJS_InitializeEngine, exposed so PDF can make its
 // own contexts compatible with XFA or vice versa.
-void FXJS_SetRuntimeForV8Context(v8::Local<v8::Context> v8Context,
-                                 IJS_Runtime* pIRuntime);
+void FXJS_SetEngineForV8Context(v8::Local<v8::Context> v8Context,
+                                CFXJS_Engine* pEngine);
 #endif  // PDF_ENABLE_XFA
 
-// Called after FXJS_InitializeRuntime call made.
+// Called after FXJS_InitializeEngine call made.
 int FXJS_Execute(v8::Isolate* pIsolate,
                  const CFX_WideString& script,
                  FXJSErr* perror);
 
 v8::Local<v8::Object> FXJS_NewFxDynamicObj(v8::Isolate* pIsolate,
-                                           IJS_Runtime* pJSContext,
+                                           CFXJS_Engine* pEngine,
                                            int nObjDefnID,
                                            bool bStatic = false);
 v8::Local<v8::Object> FXJS_GetThisObj(v8::Isolate* pIsolate);
diff --git a/testing/js_embedder_test.cpp b/testing/js_embedder_test.cpp
index 5927d89..1b21fe0 100644
--- a/testing/js_embedder_test.cpp
+++ b/testing/js_embedder_test.cpp
@@ -21,12 +21,12 @@
   v8::Isolate::Scope isolate_scope(m_pIsolate);
   v8::HandleScope handle_scope(m_pIsolate);
   FXJS_PerIsolateData::SetUp(m_pIsolate);
-  FXJS_InitializeRuntime(m_pIsolate, nullptr, &m_pPersistentContext,
-                         &m_StaticObjects);
+  FXJS_InitializeEngine(m_pIsolate, nullptr, &m_pPersistentContext,
+                        &m_StaticObjects);
 }
 
 void JSEmbedderTest::TearDown() {
-  FXJS_ReleaseRuntime(m_pIsolate, &m_pPersistentContext, &m_StaticObjects);
+  FXJS_ReleaseEngine(m_pIsolate, &m_pPersistentContext, &m_StaticObjects);
   m_pPersistentContext.Reset();
   EmbedderTest::TearDown();
   m_pIsolate->Dispose();