Subj : Re: about defining object...
To   : Youngsun Jeong <celleris@naver.com>
From : Brendan Eich <brendan@meer.net>
Date : Wed Oct 01 2003 11:18 am

Youngsun Jeong wrote:

>And I write a native constructor:
>
>//native constructor
>static JSBool
>MyObj(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval
>*rval)
>{
>    if(argc == 0)
>    {
>        obj = NULL;
>  
>

It seems better for your constructor to make a new object of your class, 
even when called with no arguments.

>    }
>    else
>    {
>        if(!js_ValueToObject(cx, argv[0], &obj))
>            return JS_FALSE;
>    }
>  
>

This makes your constructor, whether called via new or not, convert its 
argument to an object and return that.  That's wrong.  If a script calls 
'new myobject(42)', you should construct an object of my_class and give 
it an age, perhaps 42.

In other words, you should call JS_IsConstructing(cx) (see below for 
more) early, and if not constructing (if not called via operator new), 
then consider doing an argument conversion.

>    if(!obj)
>    {
>        JS_ASSERT(!argc || JSVAL_IS_NULL(argv[0]) ||
>JSVAL_IS_VOID(argv[0]));
>        if (cx->fp->flags & JSFRAME_CONSTRUCTING)
>            return JS_TRUE;
>  
>

Again, you should *not* include "jscntxt.h" and use cx->fp or any other 
member.  Use JS_IsConstructing(cx).

>        obj = js_NewObject(cx, &my_class, NULL, NULL);
>       
>        if (!obj)
>            return JS_FALSE;
>  
>

Here you can JS_SetPrivate to associate an age with the new obj.  
Perhaps the age can come from argv[0].

/be

.