getter & setter for private objects

Brendan Eich brendan at
Mon Nov 2 10:17:41 PST 2009

On Nov 2, 2009, at 2:34 AM, memolus at wrote:

> I like to use getter and setter on private objects (e.g. "var test").

That is very unclear; I'm guessing you mean getters and setters  
instead of plain variables in closures used to store private data.

> I didn't found any way to do this. I don't need sth. like
> Object.definePrivateProperty, because I only want to set getter and
> setter when I define the private object.
> Example proposal:
> var test;
> get test = function() { [..] };
> set test = function(newval) { [..] };
> I'll be pleased to hear your feedback.

Defining accessors on an activation object is nasty, it makes  
analyzing for effects hard (consider the arguments object, which is an  
indirect accessor -- both get and set -- of formal parameter values).

I doubt we'll ever standardize any such thing; Mozilla would not  
implement it even experimentally.

If you want private getters and setters, you can put them in an object  
denoted by a private var:

function make() {
   var obj = {
     get test() /* cheap fetch of x here */,
     set test(x) /* cheap update from x here */
   function validate(x) { /* expensive check of x here */ }
   return {
     get test()  { return obj.test; },
     set test(x) { validate(x); obj.test = x; }
     // etc.


More information about the es-discuss mailing list