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WeakSet

WeakSet

Introduction

WeakSet is a Set variant where values must be objects and references are weak — if no other references exist, the object can be garbage collected and automatically removed.

Basic Usage

const ws = new WeakSet();
let user = { name: 'Alice' };

ws.add(user);
console.log(ws.has(user)); // true

user = null; // Auto-removed from WeakSet!

Limitations

Values must be objects (no primitives)
No iteration methods (no .forEach(), no for...of)
No .size property
Only .add(), .has(), .delete() available

Use Cases

// Prevent double-processing
const processed = new WeakSet();
function processItem(item) {
  if (processed.has(item)) return;
  processed.add(item);
  // process...
}

// Track visited nodes in graph
const visited = new WeakSet();
function dfs(node) {
  if (visited.has(node)) return;
  visited.add(node);
  for (const n of node.neighbors) dfs(n);
}

WeakSet vs Set

Feature	Set	WeakSet
Values	Any type	Objects only
References	Strong	Weak
Iterable	✅	❌
Size	✅	❌

Further Reading