Private Names in 'text/javascript'

David Herman dherman at mozilla.com
Tue May 17 19:05:30 PDT 2011


Yes, I agree that separating them out is a good idea. Allen and I have been working on this lately, and I've signed up to present private names at the upcoming face-to-face. Our thinking has been along similar lines to what you describe here.

Dave

On May 17, 2011, at 6:55 PM, Luke Hoban wrote:

> The Private Names strawman currently combines a new runtime capability (using both strings and private names as keys in objects) with several new syntactic constructs (private binding declarations, #.id).  At the March meeting, I recall there was some support for the idea of separating these two aspects, and exposing the runtime capability also as a library that could be used in ‘text/javascript’. 
>  
> I added a comment to the Private Names strawman page to suggest how this could be done.  The runtime behavior of the proposal is the same, but in addition, a  library function “Object.createPrivteName(name)” is added which provides direct access to the internal CreatePrivateName abstract operation.  This allows the use of private names in a more verbose form, but without needing new syntax – similar in spirit to the ES5 Object.* operations.
> Borrowing an example from the current proposal to illustrate:
>  
> Using ‘text/harmony’ syntax:
> function Point(x,y) {
>    private x, y;
>    this.x = x;
>    this.y = y;
>    //... methods that use private x and y properties
> }
> var pt = new Point(1,2);
>  
> Using ‘text/javascript’ syntax:
> function Point(x,y) {
>    var _x = Object.createPrivateName("x");
>    var _y = Object.createPrivateName("y");
>    this[_x] = x;
>    this[_y] = y;
>    //... methods that use private _x and _y properties
> }
> var pt = new Point(1,2);
>  
> There seem to be several benefits to this:
> (1) The private name capability can be made available to ‘text/javascript’
> (2) The feature is easily feature-detectable, with a fallback of using ‘_’-prefixed or similar pseudo-private conventions
> (3) The core functionality can potentially be agreed upon and implemented in engines earlier than full new syntax
>  
> Luke
>  
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