reduxjs/react-redux · critical

uSES not initialized!

Error message

uSES not initialized!

What it means

react-redux lazily assigns the real useSyncExternalStore implementation from use-sync-external-store into a mutable holder; notInitialized is the placeholder it installs until initialization. If any hook runs before setBatch/initialization (or the shim failed to load), this placeholder is invoked and throws.

Source

Thrown at src/utils/useSyncExternalStore.ts:5

import type { useSyncExternalStore } from 'use-sync-external-store'
import type { useSyncExternalStoreWithSelector } from 'use-sync-external-store/with-selector'

export const notInitialized = () => {
  throw new Error('uSES not initialized!')
}

export type uSES = typeof useSyncExternalStore
export type uSESWS = typeof useSyncExternalStoreWithSelector

View on GitHub (pinned to 16f1a91eb2)

Solutions

1. Update react-redux (and use-sync-external-store) to matching latest versions
2. Clear bundler cache and rebuild; check for duplicate react-redux installs with npm ls react-redux
3. Remove any aliases or manual imports of react-redux internals / use-sync-external-store
4. If using React 18+, rely on React's built-in useSyncExternalStore path by upgrading

Example fix

// before (aliased shim)
alias: { 'use-sync-external-store': false }
// after
npm i react-redux@latest use-sync-external-store@latest
// remove alias, rebuild

// before app startup, sanity-check the shim initialized
import { unstable_batchedUpdates } from 'react-dom'
import { setBatch } from 'react-redux'
setBatch(unstable_batchedUpdates)

function isUseSyncExternalStoreReady(fn: unknown): boolean {
  return typeof fn === 'function' && fn.name !== 'notInitialized';
}

try {
  const value = useSelector(selector)
} catch (e) {
  if (e.message.includes('uSES not initialized')) {
    console.error('Broken use-sync-external-store resolution: dedupe deps and rebuild')
  }
  throw e
}

When it happens

Trigger: Using useSelector/useSyncExternalStore before react-redux's internal initialization runs — usually caused by bundler/tree-shaking producing an incorrect module evaluation order, multiple react-redux copies, or a broken/partial build of use-sync-external-store.

Common situations: Aggressive bundler optimizations (e.g. side-effect-free reordering) with older webpack/rollup setups, ESM/CJS interop issues with use-sync-external-store, or patching/aliasing react-redux internals.

Related errors

• Invalid value of type ${typeof arg} for ${name} argument whe
• Unexpected value for ${methodName} in connect.
• could not find react-redux context value; please ensure the
• You must pass a selector to useSelector
• You must pass a function as a selector to useSelector

AI-assisted analysis of reduxjs/react-redux@16f1a91eb2 (2026-08-31). Data as JSON: /api/errors/b8bfa599fa559d81. Report an issue: GitHub.