State Management Decisions

State Management Decisions

Purpose

Classify each piece of state by source and place it in exactly one home. Most "state management problems" are actually misclassification problems — server state in a global store, UI state duplicated across components, derivable values stored as state.

Universal — the source-classification model (derivable / URL / server / local / shared) applies to any reactive framework; only the tool names per category differ.

Procedure

1. Classify every piece of state by source

   Source	What to do	Example
   Derivable	Don't store — compute from input	fullName from firstName + lastName
   URL-appropriate	Sync to URL query params	filters, tabs, page number, modal open state for shareable links
   Server data	Server-state cache library	API responses, cached lists
   Local component	Framework's local state primitive	form draft, hover state, single-component UI
   Shared / global	Cross-component store with selector pattern	theme, current user object, cross-page UI state

   • Buckets compose — don't force a whole feature into one: a search page's query is URL state that drives a server fetch; classify each layer (the query string vs. the fetched results) to its own home.

2. Detect derivable state — the highest-leverage fix (eliminated state can't desync)

   • Two patterns to find: (a) an effect that writes state derived from props/other state (useEffect.*setX), and (b) a state value that merely mirrors a prop or is recomputed each render
   • Replace with a computed value (memoize only if the computation is genuinely expensive)

3. Identify missing URL state

   • Tabs, filters, pagination, sort order, modal open/close (when shareable matters)
   • Symptom: refreshing the page loses the user's place
   • Fix: lift to URL via nuqs or useSearchParams

4. Identify server-state-in-global-store

   • Anti-pattern: useStore holds users[] fetched from API
   • Why bad: cache invalidation becomes your problem, no built-in stale/loading state
   • Fix: move to TanStack Query / SWR / Apollo

5. Collapse related local-state atoms into one unit

   • 3+ interdependent local-state values in one component → consolidate into a single reducer (or a small local store)
   • Especially for wizards and complex async sequences
   • For forms specifically: prefer a form library + schema validation over a hand-rolled reducer once you have > 3 fields or any validation (see form-ux skill)

6. Move frequently-changing shared values off a broad-subscription primitive

   • A shared value that changes often and is read by many components causes excessive re-renders if it lives in a broad-subscription context
   • Move it to a selector-based store so each consumer subscribes only to the slice it needs
   • Keep broad context for rarely-changing values: theme, locale, auth identity

7. Apply optimistic UI for instant-feedback mutations

   • Mutations where the user expects immediate feedback (like-button, comment-post, drag-reorder)
   • Render the optimistic result immediately; roll back on server error

8. Document decisions

   • For non-trivial state: comment why this tool was chosen
   • Optionally: ADR for the global state architecture

Completion Criteria

• Derivable state = 0 (no useEffect syncing derived values)
• URL-appropriate state lives in URL (refresh-resilient)
• Prop drilling depth ≤ 2 (deeper → lift to a shared store or context)
• Server state in a server-state cache library (TanStack Query / SWR / Apollo), not a general client store
• State classification recorded for non-trivial cases

Output

• Refactored state code: each piece classified and moved to its correct home (URL / server / local / shared)
• ADR: docs/adr/ADR-NNN-state-management-strategy.md if introducing or changing the global store choice (see decision-records skill)
• Inline comments: // state: [server|url|local|shared] because [reason] at non-obvious state declarations
• PR description block:

  - Derived state eliminated: N
  - URL state added: N (filter / tab / page / modal)
  - Server state moved to TanStack/SWR: N
  - Prop drilling fixed (max depth: was N → now ≤ 2)
  

Implementation

React + Next.js (default)

Other stacks

• Vue / Nuxt: URL → useRoute().query + definePageMeta; Server → TanStack Query (Vue) / VueUse useFetch; Local → ref/reactive; Shared → Pinia (with defineStore + getters acting as selectors)
• SvelteKit: URL → $page.url.searchParams + goto(); Server → TanStack Query (Svelte) / SvelteKit +page.ts load; Local → Svelte 5 $state runes; Shared → Svelte stores or context API
• Angular: URL → Router + ActivatedRoute.queryParams; Server → TanStack Query (Angular) or RxJS service; Local → component property / signal; Shared → service with signals or NgRx for complex cases
• Universal anti-pattern: server state in a global store. Use a server-state library — every modern framework has TanStack Query bindings.

Related skills

• form-ux — for form state specifically (use react-hook-form over useReducer)
• api-caching-optimization — when the state is actually server data
• architecture-improvement — for cross-module state placement

Reference

• Key insight encoded: Classify state by source before picking a tool. Server state → TanStack Query (not Zustand — TanStack handles cache/stale/loading for free). URL state → nuqs (shareable, refresh-resilient). Local complex (forms/wizards) → useReducer. Cross-component client → Zustand. Reaching for a global store before this triage is an architectural smell.