diff --git a/source/CJSEngine.cpp b/source/CJSEngine.cpp
index 716d9f5be..3de2c513a 100644
--- a/source/CJSEngine.cpp
+++ b/source/CJSEngine.cpp
@@ -59,7 +59,8 @@ auto CJSEngine::Startup() -> void
 	if (!JS_Init())
 	{
 		throw new std::runtime_error("Unable to initialise JavaScript engine");
-  }
+	}
+	jsInitialized = true;
 
 	runtimeList.push_back( new CJSRuntime( engineMaxBytes ));	// Default Runtime
 	//runtimeList.push_back( new CJSRuntime( engineMaxBytes ));	// Console Runtime
@@ -70,16 +71,30 @@ auto CJSEngine::Startup() -> void
 //===================================================================
 CJSEngine::~CJSEngine()
 {
-	// Why?  we are shutting down, the process memory will take care of this for us in theory
-	/*
+	Shutdown();
+}
+
+//o------------------------------------------------------------------------------------------------o
+//| Function    -   CJSEngine::Shutdown()
+//o------------------------------------------------------------------------------------------------o
+//| Purpose     -   Releases all JavaScript runtimes before shutting down SpiderMonkey
+//o------------------------------------------------------------------------------------------------o
+void CJSEngine::Shutdown( void )
+{
 	for( RUNTIMELIST_ITERATOR rIter = runtimeList.begin(); rIter != runtimeList.end(); ++rIter )
 	{
-		if(( *rIter))
+		if(( *rIter ) != nullptr )
 		{
 			delete ( *rIter );
 		}
 	}
-	*/
+	runtimeList.clear();
+
+	if( jsInitialized )
+	{
+		JS_ShutDown();
+		jsInitialized = false;
+	}
 }
 
 void CJSEngine::Reload( void )
diff --git a/source/CJSEngine.h b/source/CJSEngine.h
index 20abbbd9b..7296df051 100644
--- a/source/CJSEngine.h
+++ b/source/CJSEngine.h
@@ -94,6 +94,7 @@ class CJSEngine
 	typedef std::vector<CJSRuntime *>::const_iterator	RUNTIMELIST_CITERATOR;
 
 	RUNTIMELIST											runtimeList;
+	bool											jsInitialized = false;
 
 public:
 
@@ -101,6 +102,7 @@ class CJSEngine
 	~CJSEngine();
 
 	auto Startup() -> void;
+	void		Shutdown( void );
 	
 	JSRuntime *	GetRuntime( UI08 runTime ) const;
 	JSContext * GetContext( UI08 runTime ) const;
diff --git a/source/CJSMapping.cpp b/source/CJSMapping.cpp
index 5af4e70c6..d84a233ac 100644
--- a/source/CJSMapping.cpp
+++ b/source/CJSMapping.cpp
@@ -39,7 +39,17 @@ CJSMapping::CJSMapping()
  */
 CJSMapping::~CJSMapping()
 {
-	//Cleanup();
+	Shutdown();
+}
+
+//o------------------------------------------------------------------------------------------------o
+//| Function    -   CJSMapping::Shutdown()
+//o------------------------------------------------------------------------------------------------o
+//| Purpose     -   Releases all script mappings and their persistent JavaScript roots
+//o------------------------------------------------------------------------------------------------o
+void CJSMapping::Shutdown( void )
+{
+	Cleanup();
 }
 
 //o------------------------------------------------------------------------------------------------o
diff --git a/source/CJSMapping.h b/source/CJSMapping.h
index 522fffeb3..112500316 100644
--- a/source/CJSMapping.h
+++ b/source/CJSMapping.h
@@ -54,10 +54,10 @@ class CJSMappingSection
 class CJSMapping
 {
 private:
-	CJSMappingSection *				mapSection[SCPT_COUNT];
+	CJSMappingSection *				mapSection[SCPT_COUNT]{};
 
-	CEnvoke *						envokeById;
-	CEnvoke *						envokeByType;
+	CEnvoke *						envokeById = nullptr;
+	CEnvoke *						envokeByType = nullptr;
 
 	void				Cleanup( void );
 	void				Parse( SCRIPTTYPE toParse = SCPT_COUNT );
@@ -67,6 +67,7 @@ class CJSMapping
 public:
 	CJSMapping() = default;
 	~CJSMapping();
+	void				Shutdown( void );
 	void				ResetDefaults( void );
 
 	void				Reload( UI16 scriptId = 0xFFFF );
diff --git a/source/cScript.cpp b/source/cScript.cpp
index 28f22f4fa..a91c7147e 100644
--- a/source/cScript.cpp
+++ b/source/cScript.cpp
@@ -12,6 +12,7 @@
 #include "StringUtility.hpp"
 #include "osunique.hpp"
 #include <jsapi.h>
+#include <js/CallAndConstruct.h>
 #include <js/Object.h>
 #include <js/CompilationAndEvaluation.h>
 #include <js/SourceText.h>
@@ -19,11 +20,28 @@
 #include <js/ErrorReport.h>
 #include <js/Exception.h>
 #include <js/GCVector.h>
+#include <js/PropertyAndElement.h>
 #include <js/ValueArray.h>
 #include <js/Warnings.h>
 
 static constexpr SI08 RV_NOFUNC = -1;
 
+static bool IsOwnScriptFunction( JSContext *cx, JS::HandleObject scriptObject, const char *functionName )
+{
+	if( functionName == nullptr )
+		return false;
+
+	bool hasOwnProperty = false;
+	if( !JS_HasOwnProperty( cx, scriptObject, functionName, &hasOwnProperty ) || !hasOwnProperty )
+		return false;
+
+	JS::RootedValue functionValue( cx );
+	if( !JS_GetProperty( cx, scriptObject, functionName, &functionValue ))
+		return false;
+
+	return functionValue.isObject() && JS::IsCallable( &functionValue.toObject() );
+}
+
 //o------------------------------------------------------------------------------------------------o
 //|	File		-	cScript.cpp
 //|	Date		-	August 26th, 2000
@@ -519,11 +537,14 @@ void cScript::Stop( void )
 
 bool cScript::InvokeEvent( const char* name, unsigned int argc, const JS::Value* argv, JS::Value* rval )
 {
+	JS::RootedObject rootedObj( targContext, targObject );
+	if( !IsOwnScriptFunction( targContext, rootedObj, name ))
+		return false;
+
 	CActiveScriptGuard activeScriptGuard( JSMapping, this );
 #if defined UOX_DEBUG_MODE
 	Console.Log( oldstrutil::format( "Triggering event '%s' from script %d", name, GetScriptID() ) );
 #endif
-	JS::RootedObject rootedObj( targContext, targObject );
 	JS::RootedValueVector rootedArgs( targContext );
 	if( argc > 0 && !rootedArgs.append( argv, argc ))
 	{
@@ -617,13 +638,8 @@ bool cScript::OnStop( void )
 //o------------------------------------------------------------------------------------------------o
 bool cScript::DoesEventExist( const char *eventToFind )
 {
-	JS::RootedValue Func( targContext, JS::NullValue() );
-	JS_GetProperty( targContext, targObject, eventToFind, &Func );
-	if( Func == JS::UndefinedValue() )
-	{
-		return false;
-	}
-	return true;
+	JS::RootedObject scriptObject( targContext, targObject );
+	return IsOwnScriptFunction( targContext, scriptObject, eventToFind );
 }
 
 //o------------------------------------------------------------------------------------------------o
@@ -3970,9 +3986,8 @@ bool cScript::ExistAndVerify( ScriptEvent eventNum, std::string functionName )
 	if( NeedsChecking( eventNum ))
 	{
 		SetNeedsChecking( eventNum, false );
-		JS::RootedValue Func( targContext, JS::NullValue() );
-		JS_GetProperty( targContext, targObject, functionName.c_str(), &Func );
-		if( Func == JS::UndefinedValue() )
+		JS::RootedObject scriptObject( targContext, targObject );
+		if( !IsOwnScriptFunction( targContext, scriptObject, functionName.c_str() ))
 		{
 			SetEventExists( eventNum, false );
 			return false;
@@ -3996,9 +4011,8 @@ bool cScript::ScriptRegistration( std::string scriptType )
 	JS::RootedValue rval( targContext );
 	// ExistAndVerify() normally sets our Global Object, but not on custom named functions.
 
-	JS::RootedValue Func( targContext, JS::NullValue() );
-	JS_GetProperty( targContext, targObject, scriptType.c_str(), &Func );
-	if( Func == JS::UndefinedValue() )
+	JS::RootedObject scriptObject( targContext, targObject );
+	if( !IsOwnScriptFunction( targContext, scriptObject, scriptType.c_str() ))
 	{
 		Console.Warning( oldstrutil::format( "Script Number (%u) does not have a %s function", JSMapping->GetScriptId( targObject ), scriptType.c_str() ));
 		return false;
diff --git a/source/uox3.cpp b/source/uox3.cpp
index 22311ae7c..6cb3a3679 100644
--- a/source/uox3.cpp
+++ b/source/uox3.cpp
@@ -3400,6 +3400,15 @@ auto Shutdown( SI32 retCode ) -> void
 		cons.join();
 	}
 
+	if( JSMapping != nullptr )
+	{
+		JSMapping->Shutdown();
+	}
+	if( JSEngine != nullptr )
+	{
+		JSEngine->Shutdown();
+	}
+
 	// don't leave file pointers open, could lead to file corruption
 
 	Console.PrintSectionBegin();