Re: EcmaScript Proposal – Private methods and fields proposals.

Waldemar Horwat waldemar at
Fri Apr 13 22:26:43 UTC 2018

On 04/13/2018 01:38 AM, Sultan wrote:
> The proposal is an explainer with regards to an alternative sigil-less syntax to back private fields/methods.
>>What does private(this)[property] do?
> "private(this)[property]" and alternatively "private[property]" or "" all invoke access of a private "property" on the "this" instance of the class, symmetrical to thesyntax/function nature of both the "super" and"import" keywords.
>>How do private fields come into existence?
> Unless i've misunderstood what is meant by "come into existence" the proposals makes use of the reserved "private" keyword to define private fields i.e "private id = 1".

I was asking about what creates those fields.

>>What's private about private fields?
> Outside of a private fields provider class, private fields/methods would not be accessible.
>>How do you prevent them from being forged or stuck onto unrelated objects?
> What do you mean by this?

Writing your private field to an object that's not an instance of your class.

class A {
   private id = ...;
   private foo = ...;
   write(value) {
     private(this)["id"] = value;
     private(this)["foo"] = ... my private secret that anyone outside the class must not learn ...;

and then invoking the above write method with a this value that's not an instance of A, such as a proxy.


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