JavaScript WeakMap

A WeakMap is a collection of key-value pairs, similar to a regular Map object in JavaScript. However, there are key differences that make WeakMap unique and particularly useful in certain scenarios. The most significant distinction lies in how it handles object references.

In a WeakMap, keys must be objects, and values can be any arbitrary value. Unlike conventional Maps, WeakMaps allow the garbage collector to reclaim memory associated with keys that are no longer referenced elsewhere in the programme. This behaviour makes WeakMap very helpful in circumstances where you need to associate data with objects while allowing those objects to be trash collected.

In the below PDF we discuss about Javascript WeakMap in detail in simple language, Hope this will help in better understanding.


WeakMap Methods:

WeakMaps have methods get(), set(), delete(), and has(). For example,

const weakMap = new WeakMap();
console.log(weakMap); // WeakMap {}
let obj = {};
// adding object (element) to WeakMap
weakMap.set(obj, 'hello');
console.log(weakMap); // WeakMap {{} => "hello"}
// get the element of a WeakMap
console.log(weakMap.get(obj)); // hello

// check if an element is present in WeakMap
console.log(weakMap.has(obj)); // true
// delete the element of WeakMap
console.log(weakMap.delete(obj)); // true
console.log(weakMap); // WeakMap {}

Advantages of WeakMap:

  • Garbage Collection Friendly: The weak references in WeakMap make it suitable for scenarios where automatic memory management is vital. When the key object is no longer referenced elsewhere, it can be efficiently removed from the WeakMap during garbage collection.
  • Reduced Memory Leaks: Using WeakMap helps prevent unintentional memory leaks. Since the key references are weak, the associated values are automatically released when the key objects are no longer in use.

Related Question

A WeakMap is a built-in object in JavaScript that provides a way to create a collection of key-value pairs where the keys are objects and the values can be arbitrary values.

Unlike a regular Map, a WeakMap only allows objects as keys, and the references to the keys are held weakly. This means that if there are no other references to a key object, it can be automatically garbage-collected.

No, WeakMaps do not have a clear method like Maps do. Once a key is no longer referenced elsewhere, its entry will be automatically removed during garbage collection.

No, WeakMaps have specific use cases, and their behavior, such as the weak references to keys and lack of direct iteration methods, makes them more suitable for certain scenarios, like private data storage or attaching metadata to objects without affecting their lifecycle.


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