Immer

Immer — immutable state with mutable API via structural sharing.

App UtilsSimple

Stack Components

LibraryImmer 10.x

Why

Write mutable code, get immutable results, no spread hell, built into Redux Toolkit. Utility libraries (lodash, date-fns, zod) save 100s of hours of boilerplate.

Zod reached 5M weekly npm downloads in 2024 as runtime validation became essential with TypeScript-first APIs.

When

Use for immutable state updates. Avoid for performance-critical hot paths.

How

1. npm install immer 2. produce(state, draft => { ... }) 3. Mutate draft 4. Get new state 5. Add environment configuration — cp .env.example .env && edit values 6. Run tests — npm test or pnpm test to verify setup 7. Deploy — git push to trigger CI/CD or manual deploy

Example

import { produce } from 'immer'; const next = produce(state, draft => { draft.user.name = 'Alice'; });

Common Problems

⚠Performance — use enableMapSet for Map/Set
⚠Freezing in dev — use setAutoFreeze(false) for perf
⚠Configuration drift between environments — use infrastructure-as-code (Terraform/Pulumi) to keep dev/staging/prod identical

Best Practices

✓Use produce for reducers
✓Leverage original() for identity checks
✓Set up health checks and graceful shutdown — handle SIGTERM to drain in-flight requests before exit

FAQ

What is Immer and what projects is it for?

Immer — immutable state with mutable API via structural sharing. It pairs layered technologies for end-to-end type safety and out-of-the-box deploys, fitting everything from MVPs to production SaaS.

How do I spin up a working demo with Immer in 10 minutes?

Two steps: (1) npm install immer; (2) produce(state, draft => { ... }). Get the local dev server running, then wire one real data source to verify the end-to-end loop.

What is the most common pitfall with Immer and how do I avoid it?

The most common pitfall is: Performance — use enableMapSet for Map/Set. Avoid it by adding the matching checklist to your PR template and running type-check + lint + unit tests in CI — three gates before merge.

What are the best practices for Immer?

Best practices for Immer include: Use produce for reducers; Leverage original() for identity checks; Set up health checks and graceful shutdown — handle SIGTERM to drain in-flight requests before exit. The first one — "Use produce for reducers" — should be set up at project init to avoid costly rework later.

When should I NOT choose Immer?

Pick something else in three cases: (1) the team has zero experience with the core framework and the deadline is tight (learning-curve risk); (2) it's a pure content/marketing site (Astro is lighter); (3) you need very high throughput (>10k RPS) or strict-consistency microservices (Go/Rust). Immer shines for mid-to-high complexity full-stack and API work — don't over-engineer simple static pages with it.