Actual WeakSet Use Cases

[Andy Earnshaw]

This is pretty much what I used it for in a previous job role. We loaded
and unloaded various iframes, registering APIs and custom elements inside
them, adding the `window` object to a WeakSet so the initialisation only
ran once.

On Tue, 23 Apr 2019 at 10:26, Andrea Giammarchi <andrea.giammarchi at gmail.com>
wrote:

> WeakSet can be very useful in general to avoid *any* object to be
> visited/setup twice, not just those coming from user-land classes.
>
> Circular references, mixins, DOM nodes one-off events handling, and so on
> and so fort.
>
> On Mon, Apr 22, 2019 at 8:26 PM #!/JoePea <joe at trusktr.io> wrote:
>
>> (I edited the broken format of my previous post)
>>
>> What other use cases are there?
>>
>> On Mon, Apr 22, 2019 at 11:20 AM #!/JoePea <joe at trusktr.io> wrote:
>>
>>> > WeakSets are perfect for branding and are how I would expect web
>>> platform class branding to be explained.
>>> >
>>> > ```js
>>> > const foos = new WeakSet();
>>> >
>>> > class Foo {
>>> >   constructor() {
>>> >     foos.add(this);
>>> >   }
>>> >
>>> >   method() {
>>> >     if (!foos.has(this)) {
>>> >       throw new TypeError("Foo.prototype.method called on an
>>> incompatible object!");
>>> >     }
>>> >   }
>>> > }
>>> > ```
>>>
>>> Just curious, is that effectively the same as what the (current)
>>> [private fields proposal](https://github.com/tc39/proposal-class-fields)
>>> offers?
>>>
>>> ```js
>>> class Foo {
>>>   #isFoo = true
>>>
>>>   method() {
>>>     if (this.#isFoo) {
>>>       throw new TypeError("Foo.prototype.method called on an
>>> incompatible object!");
>>>     }
>>>   }
>>> }
>>> ```
>>>
>>> - Joe
>>>
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