Immutable.js
Persistent immutable data structures for JavaScript — List, Map, OrderedMap, Set, Stack, Record. Immutable.js uses structural sharing so operations that 'modify' data return new versions that share unchanged subtrees, making immutability memory-efficient. Common in Redux state management and React applications where reference equality enables fast change detection.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Local data structure library. Immutability prevents accidental data modification — a security benefit for shared state in agent systems.
⚡ Reliability
Best When
You're already in an Immutable.js codebase or need the structural sharing guarantees for undo/redo or very large shared state trees.
Avoid When
Starting a new project — use immer.js for immutable updates with plain JavaScript objects and no conversion overhead.
Use Cases
- • Manage complex agent state in React/Redux applications where immutable updates enable reference equality checks and prevent accidental mutation
- • Build undo/redo systems in agent UIs using persistent data structures where every state version is a cheap structural share of the previous
- • Prevent accidental state mutation bugs in agent workflows by wrapping shared data in Immutable Maps/Lists that throw on modification
- • Optimize React shouldComponentUpdate with Immutable.is() equality checks that are O(1) for unchanged subtrees
- • Process large datasets in agent pipelines where many transformations share common substructures — structural sharing reduces memory vs copying
Not For
- • New JavaScript projects — immer.js provides immutability with normal JavaScript syntax and is significantly simpler; prefer immer for new code
- • Interop-heavy codebases — Immutable.js types don't interop with plain JavaScript without .toJS() conversion, adding friction at boundaries
- • Performance-critical tight loops — Immutable.js persistent data structures have overhead vs native arrays/objects for read-heavy access patterns
Interface
Authentication
No authentication — local data structure library.
Pricing
Immutable.js is open source and free, created by Facebook.
Agent Metadata
Known Gotchas
- ⚠ Immutable.js Maps and plain JavaScript objects are not interchangeable — JSON.stringify(immutableMap) produces '{}' not the expected JSON; always call .toJS() or .toJSON() first
- ⚠ Immutable 4.x changed TypeScript types significantly from 3.x — Map.get() now returns V | undefined instead of V; update type guards when upgrading
- ⚠ Deeply nested updates require .updateIn(['a', 'b', 'c'], fn) or .setIn(['a', 'b', 'c'], val) — forgetting the path format causes silent failures
- ⚠ Immutable.is() does value equality, not reference equality — using === on Immutable objects checks reference (will be false for equal values)
- ⚠ Records must define a schema upfront and don't support dynamic keys — use Map for dynamic key structures; mixing Record and Map patterns is confusing
- ⚠ Console.log of Immutable objects shows internal structure, not data — use .toJS() or inspect via .toObject() for readable debugging output
Alternatives
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Scores are editorial opinions as of 2026-03-07.