JavaScript WeakMap in ES8 and TypeScript

The WeakMap object stands out as a specialized entity, closely related to the Map object but with a unique twist. In this article, we'll unravel the syntax, characteristics, and methods of the JavaScript WeakMap, shedding light on its applications. Additionally, we'll delve into how to harness its capabilities in ES8 and TypeScript.

JavaScript WeakMap Object in ES8

const myWeakMap = new WeakMap([iterable]);


  • iterable: Represents an array or another iterable object whose elements are in the form of key-value pairs.

Key Points

  1. Keys of Object Type: A WeakMap object exclusively allows keys of object type. This characteristic makes it particularly suitable for scenarios where object references need to be weakly held.
  2. Garbage Collection: Similar to WeakSet, in WeakMap, if there is no reference to a key object, it becomes a candidate for garbage collection. This behavior aligns with scenarios where dynamic management of object lifetimes is crucial.
  3. Non-enumerable Keys: Keys within a WeakMap are not enumerable, meaning it doesn't provide methods to retrieve a list of keys explicitly.
  4. Iteration Order: A WeakMap object iterates its elements in insertion order, ensuring predictability in how elements are processed.

JavaScript WeakMap Methods

Let's explore the core methods provided by the WeakMap object along with their descriptions:

  1. delete(key): Deletes the specified element from the WeakMap object.
  2. get(key): Returns the value associated with the specified key.
  3. has(key): Indicates whether the WeakMap object contains the specified key.
  4. set(key, value): Adds or updates the key-value pairs in the WeakMap object.

TypeScript and ES8

Now, let's adapt the JavaScript WeakMap object to TypeScript, leveraging the benefits of static typing.

class CustomWeakMap<Key extends object, Value> {
    private weakMap: WeakMap<Key, Value>;

    constructor(iterable?: Iterable<[Key, Value]>) {
        this.weakMap = new WeakMap(iterable);

     * Deletes the specified element from the WeakMap.
     * @param {Key} key - The key to delete from the WeakMap.
     * @returns {boolean} True if the key was present and removed, false otherwise.
    delete(key: Key): boolean {
        return this.weakMap.delete(key);

     * Returns the value associated with the specified key.
     * @param {Key} key - The key to retrieve the value for.
     * @returns {Value | undefined} The value associated with the key, or undefined if not found.
    get(key: Key): Value | undefined {
        return this.weakMap.get(key);

     * Indicates whether the WeakMap contains the specified key.
     * @param {Key} key - The key to check for in the WeakMap.
     * @returns {boolean} True if the key is present, false otherwise.
    has(key: Key): boolean {
        return this.weakMap.has(key);

     * Adds or updates the key-value pair in the WeakMap.
     * @param {Key} key - The key to add or update.
     * @param {Value} value - The value to associate with the key.
    set(key: Key, value: Value): void {
        this.weakMap.set(key, value);

// Example Usage
const myTypedWeakMap = new CustomWeakMap<object, string>([{ key: { prop: 'value' }, value: 'example' }]);
const newKey = { prop: 'newValue' };
myTypedWeakMap.set(newKey, 'newExample');
console.log(myTypedWeakMap.get(newKey)); // Output: 'newExample'

In this TypeScript adaptation, the CustomWeakMap class enforces two generic types (Key and Value). This ensures that only objects can be used as keys, enhancing type safety while preserving the unique characteristics of the WeakMap. It becomes evident that this data structure offers a nuanced and specialized approach to handling key-value pairs with a unique emphasis on object references. In the evolving landscape of JavaScript collections, the WeakMap stands out as a powerful tool, closely related to the Map object but tailored for scenarios where dynamic object relationships need careful consideration.

The syntax, characteristics, and methods of the WeakMap underscore its role as a sophisticated solution for managing object references. By allowing only keys of object type, the WeakMap ensures that relationships between keys and values are flexible yet robust. The automatic garbage collection feature, akin to WeakSet, aligns with modern memory management practices, making it suitable for scenarios where object lifetimes are dynamic. In TypeScript, our adaptation of the WeakMap object in the form of the CustomWeakMap class seamlessly integrates the benefits of static typing, adding an additional layer of safety and clarity to our code. As we journey through ES8 and TypeScript, the WeakMap object shines as a testament to JavaScript's adaptability and versatility. Whether you are navigating complex object relationships or ensuring efficient memory management, the WeakMap provides a powerful and elegant solution, making it a valuable addition to the toolkit of developers exploring the frontiers of modern JavaScript.

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