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I'm not entirely done with sets and maps yet because there are specialized versions of them.

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Let me comment this out and let me introduce you to weak set and weak map.

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Now what is that?

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Let's say we have a person here,

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it's not a constant but a variable, name

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Max and I want to store it is an asset.

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Now previously we had a set of strings but of course, you can store any data in there,

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you can store objects in there as well.

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Now in the case of the weak set which I'll show you,

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it has to be object data to be precise.

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So here persons now is my new weak set which now requires objects to be stored in it,

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that means you can also store arrays in there since they are objects in the end but you can't store numbers

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or strings in there.

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So here I'll actually initialize this to be an empty set and now I can add a new entry with the add

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method and add person.

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Now right away, when you type persons., you see there are way less methods available, only add,

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delete and has. There is no method to get all the entries for example

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and the reason for that is that weak set, just like weak map which I will also show you internally works

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such that it can only store objects so that it can actually clear these objects for you, release them

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to garbage collection which I covered in the behind the scenes module,

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if you don't work with a certain piece of data anymore. Conveniently if we console log persons here,

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the browser dev tools console still allows me to look inside of that, if we reload here, we can actually

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have a look into our set and see the value here.

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Now you might wonder, why would I need this strange thing?

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Well if you have an application where you store data,

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let's say in a set, object data in a set or other arrays, where you eventually will let go of data, then

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you want to make sure that this data can be garbage collected.

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Now if we work with that person here let's say and then we do some operations with it and we

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needed it in the set for these operations and we still need the set thereafter, maybe for other operations

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but this person is not really required anymore,

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then we can set person equal to null.

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This means we set this variable to null,

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so this object no longer has anyone who is interested in it.

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This person variable, which stored its address is now reset to null,

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so the address is released from there and the Javascript engine then is able to pick this up and eventually

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clear this object from the heap,

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that's what garbage collection does, it clears that data from memory.

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Now if you would use a normal set here which you can normally, then the person you created here would

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still be part of that set.

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So even if you cleared your variable here, you added that object, that pointer at this object to this

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set and Javascript thankfully detects that and will not clear the object because the set still holds

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a reference to it and that's good because Javascript would expect that you plan on working with that

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and deleting it therefore would be bad.

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Now let's say you eventually never end up working with that person again, then with a normal set, you have

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that unnecessary data stored in memory because you have that data in a set even though you don't

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need it anymore.

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Sure, you could have done persons delete and deleted that value

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but if you forgot that, well there you go. Now with weak set,

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if you reset all other places where you point that this object, the weak set will not hold onto it.

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So the weak set allows garbage collection to delete items that are part of the set

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as long as no other part of your code uses these items,

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so now with that eventually, that will be garbage collected. Here if I reload, we can still see that person,

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so it certainly didn't get garbage collected between this line and this line but garbage collection

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can't be planned,

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you don't know when the browser does it.

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The thing is with this here and weak set being used, it's able to garbage collect this. So weak set is an

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interesting option in cases where you store object data in a set and you eventually release some of

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that data and you want to make sure that this thing can be garbage collected.

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Obviously super advanced, not something you'll use in many applications, not something we need here in

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the majority of this course

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to be honest but something to be aware of, especially as you grow as a developer and you will encounter

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more and more advanced programs,

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advanced code snippets where something like that might get used.