Re: EcmaScript Proposal – Private methods and fields proposals.

[Isiah Meadows]

If you don't need them, don't use them. The use for them is three-fold:

1. Not trusting people to avoid relying on API implementation details
(think: Node.js `_readableStream`/`_writableStream` used so frequently out
of core they've ran into issues updating it even in patch releases).
2. In the face of inheritance, avoiding name collision. (This is a big one
at scale, not so much in a 30k web app.)
3. Giving engines the ability to better structure object allocation and
property access. This is *very* useful for perf critical scenarios.

Finally, if you don't need them, don't use them. But keep in mind, there is
a use case and a need.

On Tue, Apr 17, 2018, 02:17 kai zhu <kaizhu256 at gmail.com> wrote:

> as a javascript web-developer, can someone educate me on how private
> class methods/fields would make one's life easier (rather than harder)
> in getting web-projects shipped?
>
> ```
> /*
>  * how is this cited example better than using a plain object in a
> web-project?
>  * can someone give actual common problems in
>  * debugging/integrating/shipping web-projects,
>  * that private methods/fields could help simplify (rather than
> complicate)?
>  */
> class HashTable {
>   constructor() {
>     private[Symbol.for('length')] = 0
>   }
>   set(key, value) {
>     private[key] = value
>   }
>   get(key) {
>     return private[key]
>   }
> }
> ```
>
>
> On 4/17/18, Sultan <thysultan at gmail.com> wrote:
> >>An instance has a fixed set of private fields which get created at object
> > creation time.
> >
> > The implications of this alternative does not necessarily limit the
> > creation of private fields to creation time, for example writing to a
> > private field in the constructor or at any arbitrary time within the
> > lifecycle of the instance.
> >
> > class HashTable {
> >   constructor() {
> >     private[Symbol.for('length')] = 0
> >   }
> >   set(key, value) {
> >     private[key] = value
> >   }
> >   get(key) {
> >     return private[key]
> >   }
> > }
> >
> >>How do you deal with inner nested classes wanting to refer to outer
> > classes' private fields?
> >
> > Not sure i understood what you mean by this?
> >
> >
> > On Tue, Apr 17, 2018 at 1:43 AM, Waldemar Horwat <waldemar at google.com>
> > wrote:
> >
> >> On 04/13/2018 09:41 PM, Sultan wrote:
> >>
> >>>  >Writing your private field to an object that's not an instance of
> your
> >>> class.
> >>>  >and then invoking the above write method with a this value that's not
> >>> an instance of A, such as a proxy.
> >>>
> >>> Given:
> >>>
> >>> class A {
> >>>    private id = 0;
> >>>    private method(value) {
> >>>      return value;
> >>>    }
> >>>    write(value) {
> >>>      private(this)["id"] = private["method"](value);
> >>>    }
> >>> }
> >>>
> >>> I imagine this means trying to do something along the lines of:
> >>>
> >>> (new A()).write.call({}, 'pawned');
> >>>
> >>> This would fail. The private syntax call site would be scoped to the
> >>> provider class. For example imagine the current possible transpilation
> >>> of
> >>> this:
> >>>
> >>> ;(function (){
> >>>    var registry = WeakMap();
> >>>
> >>>    function A () {
> >>>      registry.set(this, {id: 0})
> >>>    }
> >>>    A.prototype.write: function () {
> >>>      registry.get(this)["id"] =
> >>> registry.get(this.constructor)["method"].call(this,
> >>> value);
> >>>    }
> >>>
> >>>    // shared(i.e private methods)
> >>>    registry.set(A, {
> >>>      method: function (value) {
> >>>        return value;
> >>>      }
> >>>    });
> >>>
> >>>    return A
> >>> })();
> >>>
> >>> Trying to do the the afore-mentioned forge here would currently fail
> >>> along the lines of cannot read property "id" of  "undefined".
> >>>
> >>
> >> OK, so that aspect of the proposal looks the same as the existing
> private
> >> proposals — an instance has a fixed set of private fields which get
> >> created
> >> at object creation time.  There are tricky additional wrinkles when it
> >> comes to inheritance, but you can look them up in the existing
> proposals.
> >>
> >> Are the only significant changes the different property naming syntax
> and
> >> that you provide a way to map strings to private slots?  How do you deal
> >> with inner nested classes wanting to refer to outer classes' private
> >> fields?
> >>
> >>     Waldemar
> >>
> >
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