JavaScript · Map · Set · WeakMap · WeakSet

Map & Set,
finally understood

The underused siblings of Array and Object. Deduplication, fast lookups, frequency counts, and garbage-collection-safe caching — all animated with real scenarios.

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// Map — any key type, ordered, O(1) lookup
const roles = new Map([
  ['alice', 'admin'],
  ['bob',   'editor'],
]);
roles.get('alice');  // 'admin'
roles.has('bob');    // true
roles.set('carol', 'viewer');

// Set — unique values, O(1) has()
const tags = new Set(['js','css','js']);
// Set {'js', 'css'}  ← deduped!

// Deduplicate array in one line
const unique = [...new Set(arr)];