Think of a party guest list where only special guests can enter. But here’s the twist:

  • The names on the list are not written in ink, they are written in disappearing ink.
  • If a guest leaves the party and no one remembers them anymore, their name vanishes automatically from the list.

That’s what a WeakSet is in JavaScript.

What is a WeakSet?

A WeakSet is like a normal Set, but with some special rules:

  1. It only stores objects (not numbers, strings, or other primitive values).
  2. If an object is no longer referenced anywhere in the program, it will be garbage collected and automatically removed from the WeakSet.
  3. It doesn’t keep a permanent record—you can’t list out all its values.

How is it different from Set?

  • Set can store anything (numbers, strings, objects) and you can loop through it.
  • WeakSet only stores objects, and you cannot loop through its contents.

Example

let weakGuests = new WeakSet();

let guest1 = { name: "Alice" };
let guest2 = { name: "Bob" };

weakGuests.add(guest1);
weakGuests.add(guest2);

console.log(weakGuests.has(guest1)); // true

guest1 = null; // Alice leaves the party
// Automatically removed from WeakSet!

Here:

  • guest1 and guest2 are objects added to the WeakSet.
  • When guest1 is set to null, WeakSet forgets about Alice automatically.

Methods of WeakSet

  • .add(object) → adds an object
  • .has(object) → checks if object is in the set
  • .delete(object) → removes an object

Real-Life Analogy

WeakSet is like a VIP invisible guest list:

  • Only people (objects) can enter.
  • If someone leaves and no one remembers them, their name disappears.
  • You can check if someone is on the list, but you can’t see the full list.

In Short

  • WeakSet = special set for objects only.
  • Objects disappear when no longer needed.
  • Good for memory-friendly tracking of objects.

Review Questions

  1. A WeakSet is similar to a Set, but it only stores __________.
  2. If an object in a WeakSet is no longer referenced, it is automatically __________ collected.
  3. Unlike a normal Set, WeakSet cannot store __________ values.
  4. The method used to add an object to a WeakSet is __________.
  5. The method used to check if an object exists in a WeakSet is __________.
  6. The method used to remove an object from a WeakSet is __________.
  7. You cannot __________ through the contents of a WeakSet.
  8. WeakSet helps prevent __________ leaks by automatically removing unreferenced objects.
  9. A real-life analogy for WeakSet is a __________ list with disappearing ink.
  10. Normal Set can store numbers, strings, and objects, but WeakSet can only store __________.
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