View source for Plugins:NPN SetExceptionVariant

= Status =

Under consideration.

== Background ==
Unlike JavaScript the current
NPN_SetException[https://developer.mozilla.org/En/NPN_SetException] call does
not allow to throw custom objects or plain JS types as exceptions from a
plugin.  Hence the NPN_SetException limits scriptable objects to just throwing
errors with a defined message property.

== Current Proposal ==
* Last modified: July 14, 2009
* Author: Anselm R Garbe, Aplix Corporation
* Contributors:

=== NPN_SetExceptionVariant === 
One possible solution to this limitation is the introduction of a new function
call to trigger script exceptions as follows:

<pre>

void NPN_SetExceptionVariant(NPObject *npobj, const NPVariant *ex);

</pre>

The semantics of NPN_SetExceptionVariant remain similiar to NPN_SetException,
though the NPN_SetExceptionVariant call triggers a script exception upon
return from entry points into 'npobj' where the given object thrown is the 
value of 'ex'. Such a variant value may be a custom object exposing
properties, methods and type information that extends the typical 'message'
only approach and enables more fine-grain and language-independent
exception handling in JavaScript.

=== An Example === 

<pre>
bool SomeClass::invokeDefault(NPObject *npObj, const NPVariant *args, uint32_t argCount, NPVariant *result) {
        static NPVariant v;
        NPObject *ob;

        if(createCustomErrorObject(&ob) == NoError) {
                NPN_RetainObject(ob);
                OBJECT_TO_NPVARIANT(ob, v); 
                NPN_SetExceptionVariant(npObj, &v);
                return false;
        }
        INT32_TO_NPVARIANT(0, *result);
        return true;
}
</pre>

=== Legacy APIs === 

The proposed NPAPI extension works well with legacy APIs, because it doesn't
attempt to change NPN_SetException but introduces an alternative call instead.