The WeakMap is a built-in JavaScript object that provides a collection of key-value pairs where the keys must be objects, and the values can be any data type. It is similar to a Map but has some distinct characteristics:
Weak references: Unlike a Map, the keys in a WeakMap are weakly referenced. This means that if the key object has no other references, it can be garbage collected, allowing memory to be freed.
No iteration and size methods: WeakMap does not provide methods for iterating over its keys, values, or entries. Additionally, there is no size property or method available.
Limited API: The API of WeakMap is more restricted compared to Map. It only supports basic operations such as get, set, has, and delete.
To create a WeakMap instance, you can use the following syntax:
const weakMap = new WeakMap();
The WeakMap object is particularly useful when we need to associate additional data or metadata with objects without interfering with the object’s original structure. Some possible use cases include:
Private data: We can use a WeakMap to store private data associated with objects. Since the keys are weakly referenced, the private data will be automatically discarded when the associated object is garbage-collected.
Object-centric data: WeakMap can be used to store auxiliary data specific to individual objects. This can be useful when we want to attach additional information to objects without modifying their structure or introducing memory leaks.
Caching and memoization: WeakMap can be utilized for caching computed results or memoizing function calls, where the keys are function arguments, and the values are the corresponding results.
The following example demonstrates the usage of WeakMap:
let dad = { name: "Daddy" };let mom = { name: "Mommy" };const myMap = new Map();const myWeakMap = new WeakMap();myMap.set(dad);myWeakMap.set(mom);dad = null;mom = null;console.log(myMap);console.log(myWeakMap);
Lines 1–2: The variables dad and mom are initialized as objects with a name property.
Lines 4–5: The myMap variable is declared as a new Map instance, while myWeakMap is declared as a new WeakMap instance.
Line 7: The dad object is added to the myMap using the set() method of Map. Since Map uses strong references, the dad object will be retained in memory even if it goes out of scope in the subsequent lines.
Line 8: The mom object is added to the myWeakMap using the set() method of WeakMap. As WeakMap uses weak references, the mom object may be garbage-collected since there are no other references to it after the mom variable is set to null.
Lines 10–11: The dad and mom variables are set to null, meaning they no longer hold references to their respective objects.
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