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JavaScript WeakSet - GeeksforGeeks

Last Updated : 11 Jul, 2025

A WeakSet in JavaScript is a collection of unique objects where the values are weakly referenced. It works similarly to a Set, but the objects stored in a WeakSet can be garbage-collected when no longer in use.

• A WeakSet can only store objects, not primitive values like strings or numbers.
• Objects in a WeakSet can be automatically removed when they are no longer referenced elsewhere, helping to manage memory efficiently.

Syntax

const weakSet=new WeakSet()

The syntax const weakSet = new WeakSet(); initializes a new empty WeakSet in JavaScript. It creates a collection that can only store objects and automatically removes objects when they are no longer in use.

• A WeakSet can only store objects as its values. Primitive values like numbers, strings, or booleans cannot be added.
• The objects stored in a WeakSet are weakly referenced, meaning that they can be garbage-collected if there are no other references to them.
• Unlike a regular Set, you cannot iterate over the values of a WeakSet (e.g., using forEach()), as it doesn't provide methods for iteration due to weak references.
• When an object in a WeakSet is no longer referenced elsewhere, it will be automatically removed from the WeakSet, helping to avoid memory leaks.
• A WeakSet only allows unique objects, meaning the same object cannot be added multiple times. However, it doesn't allow checking the size or accessing individual elements directly.

• Objects as data: A WeakSet can only store objects, not primitive values like numbers or strings.
• Weak References: The objects in a WeakSet are weakly referenced, which means they can be garbage-collected when no longer in use.
• Uniqueness: Each object in a WeakSet must be unique; duplicate objects are not allowed.
• No Iteration: You cannot loop through or access the items in a WeakSet.
• No Size Property: Unlike other collections, a WeakSet does not provide a way to check how many items it contains.

This code demonstrates how to use a WeakSet in JavaScript to store and manage unique objects. It shows adding, checking, and removing objects, as well as how objects can be garbage collected when no longer referenced.

// Create a new WeakSet
let weakSet = new WeakSet();

// Create objects to use in the WeakSet
let obj1 = { name: "Pranjal" };
let obj2 = { name: "Pranav" };
weakSet.add(obj1);
weakSet.add(obj2);
weakSet.delete(obj1)
obj2=null
console.log(weakSet.has(obj1))
console.log(weakSet.has(obj2))

• Create a WeakSet: A new WeakSet is created using let weakSet = new WeakSet();. This will store only objects as keys.
• Add Objects: Two objects (obj1 and obj2) are created with names "Pranjal" and "Pranav", and added to the WeakSet using weakSet.add().
• Setting obj2 to null: The reference to obj2 is removed by setting it to null. Now, the object originally assigned to obj2 may be garbage collected since there are no other references to it.
• Check obj1 in WeakSet: The weakSet.has(obj1) checks if obj1 is still in the WeakSet. Since obj1 was not removed or garbage collected, it returns true.
• Check obj2 in WeakSet: The weakSet.has(obj2) checks if obj2 is in the WeakSet. Since obj2 is set to null and its object might be garbage collected, it returns false.

• add(value): Adds an object to the WeakSet. If the object is not already in the set, it is added.
• has(value): Checks if the specified object exists in the WeakSet. Returns true if it exists, otherwise false.
• delete(value): Removes the specified object from the WeakSet. Returns true if the object was removed, otherwise false.

• How to iterate over Set?
• Union of two Sets
• Intersection of two sets
• Element Ordering in a Set
• Sort a Set
• Array to Set

• Memory Management: Objects in a WeakSet can be garbage collected when no longer in use, preventing memory leaks.
• No Duplicates: A WeakSet only stores unique objects, preventing duplicate entries and ensuring efficient data storage.
• Fast Lookups: Checking if an object is in a WeakSet is efficient, with constant time complexity (O(1)).
• Automatic Cleanup: When an object is no longer referenced elsewhere, it is automatically removed from the WeakSet, reducing the need for manual cleanup.
• Private Data: WeakSet is useful for storing private data, especially for associating metadata with objects without exposing it publicly.

In conclusion, a WeakSet in JavaScript is a powerful tool for managing collections of unique objects with automatic memory management. By allowing objects to be garbage collected when no longer referenced, it helps prevent memory leaks and ensures efficient resource usage. Though limited in features like iteration, its unique properties make it ideal for specific use cases such as storing private data and improving memory efficiency.

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