Subj : Suggestion on JSErrorReporter.
To   : netscape.public.mozilla.jseng
From : J.P.
Date : Thu Sep 09 2004 12:26 pm

In SM, the current JSErrorReporter signature is defined as:

typedef void
(* JS_DLL_CALLBACK JSErrorReporter)(JSContext *cx, const char *message,
                                     JSErrorReport *report);

Often the time, the callback funtion is a static member function of a 
class. Sometimes, it is desirable to be able to know from which instance 
of that class the callback is getting called.

For example, in order to do this, I hacked the JSContext and added one 
more member variable "void* ErrorCallbackUserData".

I also changed the JS_SetErrorReporter(JSContext* cx, JSErrorReporter 
er) to JS_SetErrorReporter(JSContext* cx, JSErrorReporter er, void* 
userdata).

Now given a class:

class Foo
{
public:
	JS_Context ctx;
	const char* InstanceId;
	static void SM_ErrorReporter(JSContext *cx, const char *message, 
JSErrorReport *report);
	bool RunScript();
}

In Foo::RunScript(), I set error reporter like:
bool Foo::RunScript()
{
/*
  * I pass the pointer to this object. And I hacked the SM, so that
  * the value of this pointer will be assigned to
  * ctx->ErrorCallbackUserData.
  */
JS_SetErrorReporter(ctx, SM_ErrorReporter, (void*)this);
}

When the error callback gets called, I will know which instance of class 
  Foo is giving me trouble, like:
void Foo::SM_ErrorReporter(JSContext *cx, const char *message, 
JSErrorReport *report)
{
Foo* self = (Foo*)(cx->ErrorCallbackUserData);
printf("Instance Id: %s\n", self->InstanceId);
}

So I am suggesting to provide a mechanism to allow programmer associated 
  some kind of user data with the error reporter. Just my 2 cents.

.