What are the differences between Set, Map, WeakSet, and WeakMap?

Set, Map, WeakSet, and WeakMap

Set

A collection of unique values:

const set = new Set([1, 2, 2, 3]);
set.size; // 3
const unique = [...new Set([1, 2, 2, 3])]; // [1, 2, 3]

Map

Key-value pairs where keys can be any type:

const map = new Map();
map.set('a', 1);
map.get('a'); // 1

WeakSet

• Objects only
• Weak references — allows GC
• Not iterable, no size

WeakMap

• Object keys only
• Weak references to keys
• Not iterable, great for private data

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Comparison

Feature	Set	Map	WeakSet	WeakMap
Weak ref	❌	❌	✅	✅
Iterable	✅	✅	❌	❌
size	✅	✅	❌	❌