Subj : Re: spidermonkey watch on object.__count__
To   : Jens Thiele
From : Brendan Eich
Date : Fri Aug 27 2004 11:58 am

Jens Thiele wrote:
> now i want to call a function each time a property is added to an object
> 
> i had hoped to do this like this:
> 
> o={};
> o.watch("__count__",function(p,o,n){println("this[p]:"+this[p]+" p:"+p+"
> o:"+o+" n:"+n);return n;});
> println(o.__count__);
> o.x=10;
> println(o.__count__);
> 
> output is:
> 0
> 1
> 
> => __count__ is "incremented" but my function isn't called


__count__ is magic -- it counts the properties each time you get its 
value, as if you were calling a function to do that.


> 
> any ideas how to do this (call a function each time a property is added)?


You need more hooks than currently exist in the language itself.


> if possible in javascript - if not with additional native code (via the
> spidermonkey API without changing spidermonkey code)


You could use the jsdbgapi.h, I think.


> or should the above work and spidermonkey be fixed?


Nah, __count__ should not impose costs on ordinary property addition.

/be

> 
> Jens

.