Subj : Re: Creating Class Globally
To   : Brian Genisio
From : Brendan Eich
Date : Mon Apr 19 2004 08:26 pm

Brian Genisio wrote:
> Hey all,
> 
> Is there any way to create a Class for use in all contexts?
> 
> I have a program running with many threads, and many contexts per 
> thread.  In addition, I have about 40 classes I need to initialize using 
> JS_InitClass.  I also have a context in the main thread that is alive as 
> long as any thread is alive.


A context is for running scripts, but it is not the same thing as a 
global object.  You need a global object as the scope chain for global 
code, to hold the standard classes (Object, Date, etc.) plus your own. 
How many global objects do you have?  If you have one per context, then 
you do need to use JS_InitClass for each.


> It seems like a waste to call InitClass for _every_ context.


You mean "for every global object."

But if it were a waste, you could avoid it and leave some global objects 
without standard or custom class constructors, prototypes, etc.  How 
then would scripts work with those global objects?

The approach of using JS_SealObject on a root context's standard 
objects, before any other objects reference them, can work, but it is 
not compatible with ECMA-262, or with JS as many scripts use JS.  Once 
sealed, the object graph can't be changed at all, so you can't add 
String.prototype.sub to create a custom substring (or subscript, 
whatever) method.


> Is there a 
> way to use the classes created in the main context?  I tried this, but 
> when I try to construct an object with JS_ConstructObjectWithArguments, 
> it returns NULL for the object.


I have no idea what you did -- can you say more, or better, show code?


> Do I need to do anything to tell the context to use classes defined in a 
> different context?


Instead of worrying about pre-creating standard and/or custom classes, 
look into using JS_ResolveStandardClass and the same technique for your 
own custom classes.  See js.c.

/be

.