Subj : Re: Storing info in function objects..
To   : Chris Tchou
From : Brendan Eich
Date : Tue Jul 20 2004 09:22 am

Chris Tchou wrote:
> Is it possible to store information (a number) when defining a JS function
> that wraps a native C function, in such a way that the info can be retrieved
> from within the native C function?  This way one C function could be used
> for multiple JS functions.

Yes, XPConnect does this, and it motivated the reservation of 2 slots 
for function objects (see jsfun.c, JSCLASS_HAS_RESERVED_SLOTS(2) in 
js_FunctionClass.flags).

Use JS_SetReservedSlot to set the slot value (a number) in the function 
object when you define it, and use JS_GetReservedSlot on 
JSVAL_TO_OBJECT(argv[-2]) when your native hook is called to get the 
reserved slot value.  Reserved slot numbers start at 0, so for function 
objects, you have reserved slots 0 and 1.

/be

.