Subj : Re: How do I raise an exception?
To   : Thomas Sondergaard
From : Brendan Eich
Date : Wed Aug 03 2005 01:03 am

Thomas Sondergaard wrote:
> It seems that returning JS_FALSE from a JSNative c-function just results 
> in an error. How do I raise an exception? Preferably of type Error.

Just returning false without doing anything else silently terminates the 
running script.  That's not desirable generally ;-).

> I've found some prior posts that seems to indicate that JS_ReportError 
> should do this, but doesn't because of a bug.

No, you can use JS_ReportError to throw errors as exceptions, but they 
won't be localizable.  The bug you may be referring to involves the 
hardwired error numbers enumerated with other data by js.msg, and how an 
embedding can't use JS_ReportErrorNumber or related APIs with its own 
catalog of messages.

You can construct new exception objects and set them as pending 
exceptions (any value may be thrown, so you could throw a string or a 
number, or a boolean too [or null or undefined -- there, that's the list 
of types]), using JS_SetPendingException.

If you want to make an instance of Error and throw it, you'll have to 
get the value of the "Error" property of a properly initialized or 
otherwise (lazy standard class resolution) configured global object, and 
save it with a rooted pointer or jsval.

Then you can call this Error constructor function object reference with 
the JS_CallFunctionValue API, to create the exception object you wish to 
throw, passing appropriate arguments.  If that all works, set the new 
exception object reference as the pending exception and return false.

/be

.