Subj : Re: JSVAL_TO_OBJECT/JS_ValueToObject  etc.
To   : netscape.public.mozilla.jseng
From : Matthew Mondor
Date : Fri Aug 12 2005 06:08 pm

On Thu, 11 Aug 2005 23:17:03 -0600
"Weiyang Zhou" <weiyangz@nospam.com> wrote:

> I have a beginner question.
> 
> There pairs of macro and function like
> JSVAL_TO_OBJECT/JS_ValueToObject to convert between jsval and JSxxx
> type. I have read the API documentation, but still doesn't quite
> understand. Does anyone know how do I decide whether to use the macro
> or function?

If your function for instance requires a JSString/string, before using
the JSVAL_TO_STRING() function you would need to first verify that the
jsval really represents a string using JSVAL_IS_STRING().  Using
JS_ValueToString() will instead perform conversion to a JSString as
necessary even if the jsval passed to the function was not really a
string...

Using JSVAL_IS_STRING() and JSVAL_TO_STRING() might be stricter and
yield better performance, but if you want to make the function more
versatile and allow the user to call it with arbitrary types,
JS_ValueToString() is what you want.  Consider a print() function for
instance, which needs a string representation to print, user can pass an
integer or double value, or even object, which is converted to a string
before output.

Matt

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