diff --git a/demo/errorhandler/errordemo.lpr b/demo/errorhandler/errordemo.lpr
index 8d44866..7b1ef36 100644
--- a/demo/errorhandler/errordemo.lpr
+++ b/demo/errorhandler/errordemo.lpr
@@ -5,21 +5,36 @@ program errordemo;
 uses
   BrowserConsole, JS, Classes, SysUtils, Web;
 
-function DoRaise(aEvent : TJSMouseEvent) : boolean;
+Type
+
+  { TErrorApp }
+
+  TErrorApp = class
+    function DoRaise(aEvent : TJSMouseEvent) : boolean;
+    function DoHook(aEvent : TJSMouseEvent) : boolean;
+    Procedure DoRaiseJS;
+    Procedure DoRaiseJSError;
+    Procedure DoPascalException(O : TObject);
+    Procedure DoJSException(O : TJSObject);
+  private
+    procedure Run;
+  end;
+
+function TErrorApp.DoRaise(aEvent : TJSMouseEvent) : boolean;
 
 begin
   Result:=False;
   raise exception.Create('A exception');
 end;
 
-function DoHook(aEvent : TJSMouseEvent) : boolean;
+function TErrorApp.DoHook(aEvent : TJSMouseEvent) : boolean;
 
 begin
   Result:=False;
   HookUncaughtExceptions;
 end;
 
-Procedure DoPascalException(O : TObject);
+Procedure TErrorApp.DoPascalException(O : TObject);
 
 begin
   Writeln('O :',O.ClassName);
@@ -27,28 +42,30 @@ begin
     Writeln('Exception class message : ',Exception(O).Message);
 end;
 
-Procedure DoJSException(O : TJSObject);
+Procedure TErrorApp.DoJSException(O : TJSObject);
 begin
   writeln('Javascript exception: ',O.toString);
   if O is TJSError then
     Writeln('Error message : ',TJSError(O).Message);
 end;
 
-Procedure DoRaiseJS; assembler;
+Procedure TErrorApp.DoRaiseJS; assembler;
 asm
   throw new Object();
 end;
 
-Procedure DoRaiseJSError; assembler;
+Procedure TErrorApp.DoRaiseJSError; assembler;
 asm
   var e = new Error();
   e.message="My error message";
   throw e;
 end;
 
+Procedure TErrorApp.Run;
+
 begin
   // This will only work for the main program if you have set showUncaughtExceptions before rtl.run();
-  TJSHtmlButtonElement(Document.getElementById('btnhook')).OnClick:=@DoHook;
+  // TJSHtmlButtonElement(Document.getElementById('btnhook')).OnClick:=@DoHook;
   // These will not be caught (yet)
   TJSHtmlButtonElement(Document.getElementById('btn')).OnClick:=@DoRaise;
   // Uncomment this to set default exception handlers
@@ -63,4 +80,9 @@ begin
   // DoRaiseJSError;
 
   DoRaise(Nil);
+end;
+
+begin
+   With TErrorApp.Create do
+     Run;
 end.
diff --git a/packages/rtl/web.pas b/packages/rtl/web.pas
index f492e42..e273afc 100644
--- a/packages/rtl/web.pas
+++ b/packages/rtl/web.pas
@@ -55,8 +55,8 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
 *)
   TEventListenerEvent = TJSEvent;
 
-  TJSEventHandler = reference to function(Event: TEventListenerEvent): boolean;
-  TJSRawEventHandler = reference to Procedure(Event: TJSEvent);
+  TJSEventHandler = reference to function(Event: TEventListenerEvent): boolean; safecall;
+  TJSRawEventHandler = reference to Procedure(Event: TJSEvent); safecall;
 
   TJSEventTarget = class external name 'EventTarget' (TJSObject)
   public
@@ -636,7 +636,7 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
 
   { TJSDataTransferItem }
 
-  TJSDataTransferItemCallBack = reference to Procedure(aData : String);
+  TJSDataTransferItemCallBack = reference to Procedure(aData : String); safecall;
 
   TJSDataTransferItem = class external name 'DataTransferItem'  (TJSObject)
   private
@@ -712,8 +712,8 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
     Property metaKey  : Boolean Read FmetaKey;
     property dataTransfer : TJSDataTransfer Read FDataTransfer;
   end;
-  TJSDragDropEventHandler = reference to function(aEvent: TJSDragEvent) : Boolean;
-  THTMLClickEventHandler = reference to function(aEvent : TJSMouseEvent) : boolean;
+  TJSDragDropEventHandler = reference to function(aEvent: TJSDragEvent) : Boolean; safecall;
+  THTMLClickEventHandler = reference to function(aEvent : TJSMouseEvent) : boolean; safecall;
   { Various events }
 
 {$IFNDEF FIREFOX}
@@ -791,21 +791,21 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
     property Total : NativeUINT Read FTotal;
   end;
 
-  TJSPageTransitionEventHandler = reference to function(aEvent : TJsPageTransitionEvent) : boolean;
-  TJSHashChangeEventhandler = reference to function(aEvent : TJSHashChangeEvent) : boolean;
-  TJSMouseWheelEventHandler = reference to function(aEvent : TJSWheelEvent) : boolean;
-  TJSMouseEventHandler = reference to function(aEvent : TJSMouseEvent) : boolean;
-  THTMLAnimationEventHandler = reference to function(aEvent : TJSAnimationEvent) : boolean;
-  TJSErrorEventHandler = reference to function(aEvent : TJSErrorEvent) : boolean;
-  TJSFocusEventHandler = reference to function(aEvent : TJSFocusEvent) : boolean;
-  TJSKeyEventhandler = reference to function (aEvent : TJSKeyBoardEvent) : boolean;
-  TJSLoadEventhandler = reference to function (aEvent : TJSLoadEvent) : boolean;
-  TJSPointerEventHandler = reference to function(aEvent : TJSPointerEvent) : boolean;
-  TJSUIEventHandler = reference to function(aEvent : TJSUIEvent) : Boolean;
-  TJSPopStateEventHandler = reference to function(aEvent : TJSPopStateEvent) : Boolean;
-  TJSStorageEventHandler = reference to function(aEvent : TJSStorageEvent) : Boolean;
-  TJSProgressEventhandler =  reference to function(aEvent : TJSProgressEvent) : Boolean;
-  TJSTouchEventHandler = reference to function(aEvent : TJSTouchEvent) : boolean;
+  TJSPageTransitionEventHandler = reference to function(aEvent : TJsPageTransitionEvent) : boolean; safecall;
+  TJSHashChangeEventhandler = reference to function(aEvent : TJSHashChangeEvent) : boolean; safecall;
+  TJSMouseWheelEventHandler = reference to function(aEvent : TJSWheelEvent) : boolean; safecall;
+  TJSMouseEventHandler = reference to function(aEvent : TJSMouseEvent) : boolean; safecall;
+  THTMLAnimationEventHandler = reference to function(aEvent : TJSAnimationEvent) : boolean; safecall;
+  TJSErrorEventHandler = reference to function(aEvent : TJSErrorEvent) : boolean; safecall;
+  TJSFocusEventHandler = reference to function(aEvent : TJSFocusEvent) : boolean; safecall;
+  TJSKeyEventhandler = reference to function (aEvent : TJSKeyBoardEvent) : boolean; safecall;
+  TJSLoadEventhandler = reference to function (aEvent : TJSLoadEvent) : boolean; safecall;
+  TJSPointerEventHandler = reference to function(aEvent : TJSPointerEvent) : boolean; safecall;
+  TJSUIEventHandler = reference to function(aEvent : TJSUIEvent) : Boolean; safecall;
+  TJSPopStateEventHandler = reference to function(aEvent : TJSPopStateEvent) : Boolean; safecall;
+  TJSStorageEventHandler = reference to function(aEvent : TJSStorageEvent) : Boolean; safecall;
+  TJSProgressEventhandler =  reference to function(aEvent : TJSProgressEvent) : Boolean; safecall;
+  TJSTouchEventHandler = reference to function(aEvent : TJSTouchEvent) : boolean; safecall;
 
   TJSDocument = class external name 'Document' (TJSNode)
   Private
@@ -1850,7 +1850,7 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
   
   TJSCSSStyleDeclaration = class; // forward
 
-  TJSTimerCallBack = reference to procedure;
+  TJSTimerCallBack = reference to procedure; safecall;
   Theader = Array [0..1] of String;
   THeaderArray = Array of Theader;
 
@@ -2836,7 +2836,7 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
 
   TJSCanvasRenderingContext2D = Class;
 
-  THTMLCanvasToBlobCallback = Reference to function (aBlob : TJSBlob) : boolean;
+  THTMLCanvasToBlobCallback = Reference to function (aBlob : TJSBlob) : boolean; safecall;
 
   TJSHTMLCanvasElement = Class external name 'HTMLCanvasElement' (TJSHTMLElement)
   Public
@@ -3106,7 +3106,7 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
   end;
 
   { TJSXMLHttpRequest }
-  TJSOnReadyStateChangeHandler = reference to procedure;
+  TJSOnReadyStateChangeHandler = reference to procedure; safecall;
 
   TJSXMLHttpRequest = class external name 'XMLHttpRequest' (TJSXMLHttpRequestEventTarget)
   private
@@ -3455,7 +3455,7 @@ TEventListenerEvent = class external name 'EventListener_Event' (TJSObject)
   end;
 
   TJSMutationRecordArray = array of TJSMutationRecord;
-  TJSMutationCallback = reference to procedure(mutations: TJSMutationRecordArray; observer: TJSMutationObserver);
+  TJSMutationCallback = reference to procedure(mutations: TJSMutationRecordArray; observer: TJSMutationObserver); safecall;
 
   TJSMutationObserverInit = record
     attributes: boolean;