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livedash-node/.opencode/skills/vercel-react-best-practices/rules/js-tosorted-immutable.md
Kaj Kowalski 5bfd762e55 fix: comprehensive TypeScript/build fixes and modernization
- Update tsconfig to ES2024 target and bundler moduleResolution
- Add dynamic imports for chart.js and recharts (bundle optimization)
- Consolidate 17 useState into useReducer in sessions page
- Fix 18 .js extension imports across lib files
- Add type declarations for @rapideditor/country-coder
- Fix platform user types (PlatformUserRole enum)
- Fix Calendar component prop types
- Centralize next-auth type augmentation
- Add force-dynamic to all API routes (prevent build-time prerender)
- Fix Prisma JSON null handling with Prisma.DbNull
- Fix various type mismatches (SessionMessage, ImportRecord, etc.)
- Export ButtonProps from button component
- Update next-themes import path
- Replace JSX.Element with React.ReactElement
- Remove obsolete debug scripts and pnpm lockfile
- Downgrade eslint to v8 for next compatibility
2026-01-20 07:28:10 +01:00

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title, impact, impactDescription, tags
title impact impactDescription tags
Use toSorted() Instead of sort() for Immutability MEDIUM-HIGH prevents mutation bugs in React state javascript, arrays, immutability, react, state, mutation

Use toSorted() Instead of sort() for Immutability

.sort() mutates the array in place, which can cause bugs with React state and props. Use .toSorted() to create a new sorted array without mutation.

Incorrect (mutates original array):

function UserList({ users }: { users: User[] }) {
  // Mutates the users prop array!
  const sorted = useMemo(
    () => users.sort((a, b) => a.name.localeCompare(b.name)),
    [users]
  )
  return <div>{sorted.map(renderUser)}</div>
}

Correct (creates new array):

function UserList({ users }: { users: User[] }) {
  // Creates new sorted array, original unchanged
  const sorted = useMemo(
    () => users.toSorted((a, b) => a.name.localeCompare(b.name)),
    [users]
  )
  return <div>{sorted.map(renderUser)}</div>
}

Why this matters in React:

  1. Props/state mutations break React's immutability model - React expects props and state to be treated as read-only
  2. Causes stale closure bugs - Mutating arrays inside closures (callbacks, effects) can lead to unexpected behavior

Browser support (fallback for older browsers):

.toSorted() is available in all modern browsers (Chrome 110+, Safari 16+, Firefox 115+, Node.js 20+). For older environments, use spread operator:

// Fallback for older browsers
const sorted = [...items].sort((a, b) => a.value - b.value)

Other immutable array methods:

  • .toSorted() - immutable sort
  • .toReversed() - immutable reverse
  • .toSpliced() - immutable splice
  • .with() - immutable element replacement