Subj : Re: Using JS_InstanceOf with jsval's
To   : netscape.public.mozilla.jseng
From : Brendan Eich <brendan@meer.net>
Date : Tue Jan 20 2004 03:17 pm

Brendan Eich wrote:

> If you want an API to tell what the instanceof operator's result would 
> be, use this:
>
>    JSObject *b = JSVAL_TO_OBJECT(bval);
>    JSObject *B = JS_GetConstructor(cx, b);
>    JSBool answer;
>    JS_GET_CLASS(cx, B)->hasInstance(cx, B, JSVAL_TO_OBJECT(aval), 
> &answer);


I was typing from memory, but got the third argument's type wrong; Mike 
kindly set me straight in email:

   JS_GET_CLASS(cx, B)->hasInstance(cx, B, aval, &answer);

The type is jsval, not JSObject *.  This allows an object to say that it 
has any value as an instance, although currently only object values are 
considered instances of functions (class constructors whose .prototype 
property references an object on the __proto__ chain of the object value).

/be

.