v5.0.1

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Thispatch release adjusts theisPlainObject util to allow objects created viaObject.create(null), and fixes a type issue which accidentally made the store state type non-nullable.

What's Changed

• fix(isPlainObject): support check Object.create(null) by@​zhe-he in#​4633
• fix(types/store): Unexpectedly narrowed return type of functionStore['getState'] by@​exuanbo in#​4638

Full Changelog:reduxjs/redux@v5.0.0...v5.0.1

v5.0.0

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Thismajor release:

• Converts the codebase to TypeScript
• Updates the packaging for better ESM/CJS compatibility and modernizes the build output
• Requires thataction.typemust be a string
• Continues to markcreateStore as deprecated
• Deprecates theAnyAction type in favor of anUnknownAction type that is used everywhere
• Removes thePreloadedState type in favor of a new generic argument for theReducer type.

This release hasbreaking changes.

This release is part of a wave of major versions of all the Redux packages:Redux Toolkit 2.0, Redux core 5.0, React-Redux 9.0, Reselect 5.0, and Redux Thunk 3.0.

For full details on all of the breaking changes and other significant changes to all of those packages, see the"Migrating to RTK 2.0 and Redux 5.0" migration guide in the Redux docs.

[!NOTE]
The Redux core, Reselect, and Redux Thunk packages are included as part of Redux Toolkit, and RTK users do not need to manually upgrade them - you'll get them as part of the upgrade to RTK 2.0. (If you're not using Redux Toolkit yet,please start migrating your existing legacy Redux code to use Redux Toolkit today!)

### RTKnpm install @​reduxjs/toolkityarn add @​reduxjs/toolkit### Standalonenpm install reduxyarn add redux

Changelog

ESM/CJS Package Compatibility

The biggest theme of the Redux v5 and RTK 2.0 releases is trying to get "true" ESM package publishing compatibility in place, while still supporting CJS in the published package.

The primary build artifact is now an ESM file,dist/redux.mjs. Most build tools should pick this up. There's also a CJS artifact, and a second copy of the ESM file namedredux.legacy-esm.js to support Webpack 4 (which does not recognize theexports field inpackage.json). Additionally, all of the build artifacts now live under./dist/ in the published package.

Modernized Build Output

We now publish modern JS syntax targeting ES2020, including optional chaining, object spread, and other modern syntax. If you need to

Build Tooling

We're now building the package usinghttps://github.com/egoist/tsup. We also now include sourcemaps for the ESM and CJS artifacts.

Dropping UMD Builds

Redux has always shipped with UMD build artifacts. These are primarily meant for direct import as script tags, such as in a CodePen or a no-bundler build environment.

We've dropped those build artifacts from the published package, on the grounds that the use cases seem pretty rare today.

There's now aredux.browser.mjs file in the package that can be loaded from a CDN like Unpkg.

If you have strong use cases for us continuing to include UMD build artifacts, please let us know!

createStore Marked Deprecated

InRedux 4.2.0, we marked the originalcreateStore method as@deprecated. Strictly speaking,this isnot a breaking change, nor is it new in 5.0, but we're documenting it here for completeness.

This deprecation is solely avisual indicator that is meant to encourage users tomigrate their apps from legacy Redux patterns to use the modern Redux Toolkit APIs.

The deprecation results in avisual strikethrough when imported and used, likecreateStore, but withno runtime errors or warnings.

createStore will continue to work indefinitely, and willnot ever be removed. But, today we wantall Redux users to be using Redux Toolkit for all of their Redux logic.

To fix this, there are three options:

• Follow our strong suggestion to switch over to Redux Toolkit andconfigureStore
• Do nothing. It's just a visual strikethrough, and it doesn't affect how your code behaves. Ignore it.
• Switch to using thelegacy_createStore API that is now exported, which is the exact same function but with no@deprecated tag. The simplest option is to do an aliased import rename, likeimport { legacy_createStore as createStore } from 'redux'

Action typesmust be strings

We've always specifically told our users thatactions and statemust be serializable, and thataction.typeshould be a string. This is both to ensure that actions are serializable, and to help provide a readable action history in the Redux DevTools.

store.dispatch(action) now specifically enforces thataction.typemust be a string and will throw an error if not, in the same way it throws an error if the action is not a plain object.

In practice, this was already true 99.99% of the time and shouldn't have any effect on users (especially those using Redux Toolkit andcreateSlice), but there may be some legacy Redux codebases that opted to use Symbols as action types.

TypeScript Changes

We've dropped support for TS 4.6 and earlier, and our support matrix is now TS 4.7+.

Typescript rewrite

In 2019, we began a community-powered conversion of the Redux codebase to TypeScript. The original effort was discussed in#​3500: Port to TypeScript, and the work was integrated in PR#​3536: Convert to TypeScript.

However, the TS-converted code sat around in the repo for several years, unused and unpublished, due to concerns about possible compatibility issues with the existing ecosystem (as well as general inertia on our part).

Redux core v5 is now built from that TS-converted source code. In theory, this should be almost identical in both runtime behavior and types to the 4.x build, but it's very likely that some of the changes may cause types issues.

Please report any unexpected compatibility issues!!

AnyAction deprecated in favour ofUnknownAction

The Redux TS types have always exported anAnyAction type, which is defined to have{type: string} and treat any other field asany. This makes it easy to write uses likeconsole.log(action.whatever), but unfortunately does not provide any meaningful type safety.

We now export anUnknownAction type, which treats all fields other thanaction.type asunknown. This encourages users to write type guards that check the action object and assert itsspecific TS type. Inside of those checks, you can access a field with better type safety.

UnknownAction is now the default any place in the Redux source that expects an action object.

AnyAction still exists for compatibility, but has been marked as deprecated.

Note thatRedux Toolkit's action creators have a.match() method that acts as a useful type guard:

if(todoAdded.match(someUnknownAction)){// action is now typed as a PayloadAction<Todo>}

You can also use the newisAction util to check if an unknown value is some kind of action object.

Middleware type changed - Middlewareaction andnext are typed asunknown

Previously, thenext parameter is typed as theD type parameter passed, andaction is typed as theAction extracted from the dispatch type. Neither of these are a safe assumption:

• next would be typed to haveall of the dispatch extensions, including the ones earlier in the chain that would no longer apply.
  • Technically it would bemostly safe to typenext as the default Dispatch implemented by the base redux store, however this would causenext(action) to error (as we cannot promiseaction is actually anAction) - and it wouldn't account for any following middlewares that return anything other than the action they're given when they see a specific action.
• action is not necessarily a known action, it can be literally anything - for example a thunk would be a function with no.type property (soAnyAction would be inaccurate)

We've changednext to be(action: unknown) => unknown (which is accurate, we have no idea whatnext expects or will return), and changed theaction parameter to beunknown (which as above, is accurate).

In order to safely interact with values or access fields inside of theaction argument, you must first do a type guard check to narrow the type, such asisAction(action) orsomeActionCreator.match(action).

This new type is incompatible with the v4Middleware type, so if a package's middleware is saying it's incompatible, check which version of Redux it's getting its types from!

PreloadedState type removed in favour ofReducer generic

We've made tweaks to the TS types to improve type safety and behavior.

First, theReducer type now has aPreloadedState possible generic:

typeReducer<S,AextendsAction,PreloadedState=S>=(state:S|PreloadedState|undefined,action:A)=>S

Per the explanation in#​4491:

Why the need for this change? When the store is first created bycreateStore/configureStore, the initial state is set to whatever is passed as thepreloadedState argument (orundefined if nothing is passed). That means that the first time that the reducer is called, it is called with thepreloadedState. After the first call, the reducer is always passed the current state (which isS).

For most normal reducers,S | undefined accurately describes what can be passed in for thepreloadedState. However thecombineReducers function allows for a preloaded state ofPartial<S> | undefined.

The solution is to have a separate generic that represents what the reducer accepts for its preloaded state. That waycreateStore can then use that generic for itspreloadedState argument.

Previously, this was handled by a$CombinedState type, but that complicated things and led to some user-reported issues. This removes the need for$CombinedState altogether.

This change does include some breaking changes, but overall should not have a huge impact on users upgrading in user-land:

• TheReducer,ReducersMapObject, andcreateStore/configureStore types/function take an additionalPreloadedState generic which defaults toS.
• The overloads forcombineReducers are removed in favor of a single function definition that takes theReducersMapObject as its generic parameter. Removing the overloads was necessary with these changes, since sometimes it was choosing the wrong overload.
• Enhancers that explicitly list the generics for the reducer will need to add the third generic.

Other Changes

Internal Listener Implementation

The Redux store has always used an array to track listener callbacks, and usedlisteners.findIndex to remove listeners on unsubscribe. As we found in React-Redux, that can have perf issues when many listeners are unsubscribing at once.

In React-Redux, we fixed that with a more sophisticated linked list approach. Here, we've updated thelisteners to be stored in aMap instead, which has better delete performance than an array.

In practice this shouldn't have any real effect, because React-Redux sets up a subscription in<Provider>, and all nested components subscribe to that. But, nice to fix it here as well.

isAction Predicate

We recently added anisAction predicate to RTK, then realized it's better suited for the Redux core. This can be used anywhere you have a value thatcould be a Redux action object, and you need to check if it is actually an action. This is specifically useful for use with the updated Redux middleware TS types, where the default value is nowunknown and you need to use a type guard to tell TS that the current value is actually an action:

We've also exported theisPlainObject util that's been in the Redux codebase for years as well.

What's Changed

Entirely too many PRs to list here, as it's been a few years since 4.2 was released :) See the diff below.

Full Changelog:reduxjs/redux@v4.2.1...v5.0.0