Subj : Re: Missing the getProperty/setProperty mark with strings
To   : netscape.public.mozilla.jseng
From : "Sterling Bates" <sblist*nospam*serv@bigbangco.com>
Date : Sat Oct 25 2003 12:43 pm

Here's some more info:

It looks like the jsval has no JSVAL_* markers.  The error is actually
occuring when converting the jsval to an object (in the js_ValueToString
function, line 2640-2646).  If I call JS_ValueToObject from my code then I
get the same error.

I've tried both of these lines to create the JSString:

Result := jsval(JS_NewString(FContext,PChar(str),Length(str)));
Result := jsval(StringToJSString(str));

(The |str| variable is a direct reference to the Delphi object's private
field FValue.)

-> function StringToJSString:

function StringToJSString(const str: String): PJSString;
begin
  New(Result);
  Result^.length :=
MultiByteToWideChar(0,0,PChar(str),Length(str),Result^.chars,0);
  GetMem(Result^.chars,Result^.length);

MultiByteToWideChar(0,0,PChar(str),Length(str),Result^.chars,Result^.length)
;
end;

(MultiByteToWideChar is a Windows API.)

Let me know if you need anything else.

Sterling

"Sterling Bates" <sblist*nospam*serv@bigbangco.com> wrote in message
news:bne1m2$bf11@ripley.netscape.com...
> I have a Delphi object that I want to be interactive with JS and other
> Delphi code simultaneously.  Basically, a property set through JS should
be
> immediately available through Delphi & vice versa.
>
> I've been able to have JS set the string property just fine, but returning
a
> Delphi string property to javascript crashes the engine.  I'm pretty sure
> this can be done, so I'm just wondering where my error lies.
>
> 1. Creating the object.  I immediately assign a property to the associated
> JSObject called __addr which is the memory address of the Delphi class
> instance.  This works fine, the JSClass property setter & getter use this,
> and then interact with the Delphi object.
>
> 2. Setting a property.  My class setter gets the name & value of the
> variable to be set, then passes those on to the Delphi object.  This works
> great using RTTI (reflection).
>
> 3. Getting a property.  My class getter retrieves the name of the property
> to get, then passes that to the Delphi object.  I create a new JSString
(on
> the heap) containing the existing Delphi object's property value, and
return
> that as a jsval to the class getter.
>
> If I GC and shut down the context & runtime before hitting step 3,
> everything is great.  After step 3, the GC throws an access violation at
> address 6102BE7A.  I know it's my allocation of the JSString, but I don't
> know how else to handle the get operation.  I've tried looking at the
> spidermonkey code, but I can only glean a trace of what's going on there.
>
> Thanks for any help,
>
> Sterling
>
>

.