Immer
Produces immutable state by writing mutable code using JavaScript Proxy. The 'produce' function creates a draft copy that captures mutations and returns a new immutable state with structural sharing — without deep cloning. Powers Redux Toolkit's immutable state updates. Won the React Open Source award. Simplest path to immutability in JavaScript: write mutable code, get immutable results.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
MIT licensed. Zero dependencies. Proxy-based — no security concerns. Structural sharing means sensitive data may be shared between state versions; clear sensitive state explicitly.
⚡ Reliability
Best When
You're writing Redux reducers or React state updates with complex nested objects and want to write natural mutable code that produces correct immutable state.
Avoid When
You need maximum performance in a hot path where Proxy overhead matters, or your environment doesn't support ES6 Proxy (IE11).
Use Cases
- • Write clear, mutable-style state update logic in Redux reducers without complex spread operators
- • Implement immutable state updates in React's useReducer with intuitive mutation syntax via produce()
- • Build agent state machines where each state transition is written as simple mutations but produces new immutable state
- • Simplify deeply nested state updates: draft.user.preferences.theme = 'dark' vs spread-heavy alternatives
- • Implement copy-on-write data structures in agent pipelines where structural sharing is needed for performance
Not For
- • Non-JavaScript environments — Immer requires ES6 Proxy; old environments need useProxies: false with less ergonomic API
- • Performance-critical hot paths — Proxy-based drafts have overhead; for maximum performance use manual immutable patterns
- • Circular reference structures — Immer doesn't support circular references in draft state
Interface
Authentication
Local library — no authentication required. MIT licensed.
Pricing
MIT licensed. Zero cost.
Agent Metadata
Known Gotchas
- ⚠ Do NOT mix returning a new value AND mutating draft in the same recipe — if recipe returns a value, Immer uses that value; if it mutates draft (and returns undefined), Immer uses draft; mixing causes errors
- ⚠ Draft state cannot be used outside the produce() recipe — storing draft in a closure or async callback outside recipe throws ImmutableStateException
- ⚠ Map and Set require enableMapSet() plugin: import { enableMapSet } from 'immer'; enableMapSet() — not enabled by default for bundle size reasons
- ⚠ Structural sharing only works for unmodified branches — modified paths create new objects; deeply nested large objects still create new parent objects up the tree
- ⚠ TypeScript: produce<State>((draft) => { draft.x = 1 }) — draft type is Draft<State> with writable properties; read-only types become writable in draft
- ⚠ produceWithPatches() generates JSON-Patch operations alongside the new state — useful for implementing undo/redo or sync operations
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Immer.
Scores are editorial opinions as of 2026-03-06.