We now export an UnknownAction type, which treats all fields other than action.type as unknown. This encourages users to write type guards that check the action object and assert its specific 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 that Redux 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>
}

Earlier Alpha Changes

Summarizing changes from the earlier 5.0-alpha releases:

• Source code converted to TS
• createStore deprecation tag ported
• Removed isMinified check
• Packaging converted to have full ESM/CJS compatibility
• Dropped UMD build artifacts
• JS build output is now "modern" and not transpiled for IE11 compatibility
• Listener subscriptions are now a Set
• Store enhancer types improved
• Reducer type accepts a PreloadedState generic
• Middleware action and next are typed as unknown
• action.type field must be a string

What's Changed

• Prefer use of Action or UnknownAction instead of AnyAction by @EskiMojo14 in https://github.com/reduxjs/redux/pull/4520

Full Changelog: https://github.com/reduxjs/redux/compare/v5.0.0-alpha.6...v5.0.0-beta.0