What are the actual uses of ES6 WeakMap?

javascript

memoization

garbage-collection

event-listeners

byAlex Kataev·Mar 10, 2025

WeakMap is your go-to tool for optimally associating data with objects, ensuring tidy garbage collection and preventing memory leaks. It also allows you to maintain private data for objects. Here's a quick dive into it:

let weakMap = new WeakMap();
let obj = {};

// "Save your secrets here, we don't leak!"
weakMap.set(obj, { secret: 'noLeaks!' });

// "Abra-ka-dabra! Here are your secrets."
console.log(weakMap.get(obj)); // Output: { secret: 'noLeaks!' }

// "'obj'? Never heard of it!" - Garbage Collector, probably.

With a WeakMap, no manual cleanup is required to match the lifecycle of the associated data with the key object.

Leveraging WeakMaps for object extensions

WeakMaps provide a pathway to enhance objects externally while preserving their originality. Here's why you might opt for them:

Preserving object authencity

Storing metadata with WeakMaps lets you retain the integrity of user or library objects —they remain unchanged, facilitating the use of immutable data structures.

Cherishing temporary bonds

WeakMaps are valuable in applications where associations or connections are fleeting, such as tracking event listeners or monitoring resource usage.

Malleability for external capabilities

When an object needs additional features without becoming burdensome, WeakMap can provide those capabilities externally. This trick can boost performance and avoid influencing those objects that don't require these functionalities.

Economizing memory for computed results

In high-performance, real-time applications, WeakMap can be employed as a cache for computed outcomes. WeakMap is perfect for memoization techniques with critical garbage collection considerations.

Advanced scenarios for WeakMaps

Diving deep into WeakMaps, they equip you with the power to manage associated data in more complex scenarios:

Augmenting DOM elements

When wrestling with DOM elements in web development, WeakMap can attach states or behaviours without risking memory leaks, crucial when dealing with dynamically acquired nodes.

Node.js specific utilization

In the realm of Node.js, the WeakMap shines for unhandled promise rejection tracking. This assists in efficient error handling without medddling with the garbage collection, improving server performance and stability.

Libraries and unaltered object data

Writing JavaScript libraries requires caution not to modify user-provided objects. A WeakMap holds operational data without touching the original object, preserving its interface and performance.

Master planner for memory

For complex applications juggling creation and destruction of objects, a WeakMap ensures that once an object retires, its associated data doesn't overstay its welcome.

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