JavaScript WeakMap

A WeakMap is a built-in object in JavaScript that stores key-value pairs, where keys must be objects and values can be any data type. Unlike Map, WeakMap holds keys weakly, so if a key object becomes unreachable elsewhere, it can be garbage collected automatically.

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Why Use WeakMap?

• Useful for private data storage tied to objects.
• Prevents memory leaks by allowing garbage collection of unused keys.
• Keys are not enumerable — you cannot iterate over a WeakMap.
• Ideal for caching or associating metadata with objects without modifying them.

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Syntax

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Example 1: Basic Usage

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Important Points About WeakMap

• Only objects can be keys.
• WeakMap methods include set(), get(), has(), and delete().
• Keys are not iterable or enumerable.

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Example 2: Using has() and delete()

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Example 3: Private Data Encapsulation

In this example, age is private and cannot be accessed directly from outside the class.

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WeakMap vs Map

• WeakMap keys must be objects; Map keys can be any type.
• WeakMap keys are weakly referenced and not enumerable.
• Map keys are strongly referenced and enumerable.

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Key Takeaways

• Use WeakMap for storing key-value pairs with object keys only.
• WeakMaps help avoid memory leaks through automatic garbage collection.
• Suitable for private/internal data storage and caching.
• WeakMap keys are not iterable.