Subj : Re: Enumerating standard class properties & methods
To   : netscape.public.mozilla.jseng
From : "Sterling Bates" <sterlingb@bigbangmapsonco.com>
Date : Wed Dec 17 2003 02:36 pm


"Brendan Eich" <brendan@meer.net> wrote in message
news:3FE0C28F.7060300@meer.net...
> Sterling Bates wrote:
>
> > I agree that hardcoding is not always a good thing, but ruling it out
brings
> > me back to square one.  I'm not aware of another option to dynamically
> > discover the properties and methods of standard classes.
>
> If you don't need to enumerate them (JS does not), then why do you not
> simply look up any name on demand, and find whether it refers to a
> property of the global object (etc. down the object "tree" or graph)?

I don't actually need the list of methods for the bridge code to work, I
need it so that clients of the bridge will get a list of methods of all
objects when they call Enumerate on them.  Maybe it's easier to show the
code.  A TJSObject is a wrapper for any JSVAL_OBJECT (written here from
memory...):

    TJSObject = class
    private
        JSObj: PJSObject;
    public
        [...]
        function Enumerate: TStringArray;
        procedure GetProperty(const Name: String; var retval: TJSObject);
        [...]
    end;

    function TJSObject.Enumerate: TStringArray;
    var
        jslist: JSIdArray;
    begin
        jslist := JS_Enumerate(self.JSObj);
        [... parse into Delphi string array ...]
    end;

    procedure TJSObject.GetProperty(const Name: String; var retval:
TJSObject);
    var
        rval: jsval;
        jsobj: PJSObject;
        prv: Pointer;
    begin
        JS_GetProperty(Context, JSObj, PChar(Name), @rval);
        jsobj := JSValToObject(rval);
        prv := JS_GetPrivate(Context, jsobj);

        if (prv = nil) then
            retval := TJSObject.Create(JSEngine, jsobj)
        else
            retval := TJSObject(prv);
    end;

First the user calls Enumerate for the currently wrapped jsobject (say
global).  When the user gets to an item of type Object (determined
elsewhere), it calls the above GetProperty method, which wraps the property
of that name in another TJSObject, or reuses the current wrapper for that
property.  It's like reconstructing the object tree, as necessary, in
Delphi.

When a TJSObject is wrapping a Date-classed object, the .Enumerate call will
return an empty array.  The ideal is to return a list of methods, since
that's what the client expects.  That's where I'm pondering the hardcoded
list of properties.

Sterling

.