Subj : Re: Another JS question
To   : netscape.public.mozilla.jseng
From : Issac Goldstand
Date : Tue May 04 2004 12:04 pm

Continuing discussion on netscape.public.mozilla.jseng:

----- Original Message ----- 
Sent: Monday, May 03, 2004 11:06 PM
Subject: Re: Another JS question


> Issac Goldstand wrote:
>
> >Brendan,
> >  First of all, thanks tons for putting up with me a few weeks ago with
the
> >"bugs" I was finding in the SpiderMonkey API (which was really just
> >forgetting to set /OPT:NOICF on Win32)...
> >
> >I've since made a lot of progress and finding myself making good
progress...
> >
> >I'm currently trying to make glue to return objects from JS in Perl...  I
> >have a single conversion function which converts a jsval to whatever type
> >best suits it.  To do this, it does a simple switch on JS_TypeOfValue.
> >Numbers and strings were an easy start, and I qwuickly started working on
> >arrays.  Currently, I do something like:
> >
> >    case JSTYPE_OBJECT:
> >    {
> >        JSObject* obj;
> >        if (!(JS_ValueToObject(cx,v,&obj))) {
> >            return UNDEFINED;
> >        }
> >        if (JS_IsArrayObject(cx,obj)) {
> >
> >            DoArrayCallback(cx,obj);
> >        } else {
> >            return UNDEFINED;
> >        }
> >
> >
>
> Nit: return UNDEFINED early in both cases, and don't write else after
> return when you transpose the then and else parts in the second if
> statement.
>

I return UNDEFINED in the else block as a placeholder - I hope to implement
some intelligent logic for that in the future.

> Bug: JS_ValueToObject can return null in obj and true as its return
> value -- you need to check and defend, as null is not a valid object to
> pass to JS_IsArrayObject, etc.

???
But I thought " JS_ValueToObject converts a specified JS value, v, to a JS
object. The converted object is stored in the object pointed to by objp. If
the conversion is successful, JS_ValueToObject returns JS_TRUE. Otherwise it
returns JS_FALSE. "  I would think that null would be an unsuccessful
conversion

> >var a = new Array(43);
> >a["AB"] = new Array();
> >a["AB"][0] = new areaCode("780                    ", new Array(new
> >nxx("any","Any Location           "), new nxx("Edmonton","Edmonton")));
> >a["AR"] = new Array();
> >a["AR"][0] = new areaCode("501                    ", new Array(new
> >nxx("any","Any Location           "), new nxx("Ferndale","Ferndale"), new
> >nxx("Palarm","Palarm"), new nxx("Pinnacle","Pinnacle")));
> >
> >a["AR"][1] = new areaCode("479                    ", new Array(new
> >nxx("any","Any Location           "), new
nxx("Bentonville","Bentonville"),
> >new nxx("Fayetteville","Fayetteville")));
> >
> >... continues for another 41 states
> >
> >
>
> a is not an Array.  You are not indexing -- using non-negative integer
> property ids.  Why not use an Object instead?  You could even use
> convenient object literal notation (a = {AB: [...], AR: [...], ...]).
>

I'm not sure I understood that...  In any case, I can't change the
javascript source as I'm having it passed to me - not generating it myself.

> >If I then do JS_GetProperty(cx,global,"a",&rval) and pass rval to my
> >conversion function, it returns a 43member array with everything
UNDEFINED.
> >Debugging shows me that the type is 0 (I think that's JS_VOID) for each
> >recursive call beyond the top-level array.  My question is what is the
> >"proper" way to recurse into a data structure like this?
> >
> >One thought that I had was:  I currently return each element of the array
by
> >calling JS_GetArrayLength and using a for loop with JS_GetElement.  I
> >thought maybe the "hash-like" nature of the top level of the array
wouldn't
> >work with that.
> >
>
> It does not.  Arrays are objects that track their length (one greater
> than the greatest non-negative property id).  They don't allocate an
> index aliasing the named properties you add to them (they did long ago,
> in JS1.0, but that mode is not part of the ECMA standard).
>
> > Frankly, I'd rather identify hash-like arrays anyway and
> >return a proper hash-table for them.
> >
> >
>
> Use an object.
>
> To enumerate it, use a for..in loop.
>

Is there any way to identify an object that follows this "hash-like"
convention, so I can add a section in the conversion function to return a
native hash as the return value?

> >PS - If you're not the correct address for questions like this, I'll
gladly
> >send them somewhere else if you could point me to the best place.
> >
>
> You've read news://news.mozilla.org/netscape.public.mozilla.jseng,
> right?  That's the place for SpiderMonkey embedding questions.  Don't
> mail me, I may not answer, and others won't learn from my answers if I
> do reply.

I didn't read it.  I knew it was there.  I couldn't access it.  It troubled
me for a bit, but I never really applied myself to seeing why it didn't
work.  When you told me that this was really the "proper" forum for these
discussions I tried again, found out that my firewall was blocking nntp
access to any server not explicitly whitelisted and remedied the situation.
Thanks :-)

  Issac

> /be
>

.