Subj : Re: exceptions
To   : Jeroen de Borst <jeroen42@yahoo.com>
From : Brendan Eich <brendan@meer.net>
Date : Fri Mar 05 2004 11:09 am

Jeroen de Borst wrote:

>Hi,
>
>I would like my C code to throw an exception that I can then catch from the
>script that invoked it. Ideally the exception I throw would be subclassed
>from "Error" (so I'll inherit the toString() method and stack property; the
>message property would be overloaded).
>
>So I'd need to create a prototype object with the Error class defined in
>jsexn.c (ExceptionClass), and then I can use that in a call to JS_InitClass.
>But ExceptionClass is a static structure. So I don't see how to do this
>without modifying the SpiderMonkey source (which I don't want to do for
>licensing reasons).
>
>Is there another (intended) way to do this?
>

Sure, you can JS_GetProperty(cx, global, "Error", &v) to get the 
constructor, then JS_GetProperty(cx, JSVAL_TO_OBJECT(v), "prototype", 
&v), then JS_GET_CLASS(cx, JSVAL_TO_OBJECT(v)).  Error and type checking 
elided, as usual.

If this is a startup only cost,

    static const char Ep[] = "Error.prototype";
    JS_EvaluateScript(cx, global, Ep, sizeof Ep - 1, NULL, 0, &v);

is a little easier to read.

/be

.