What are Redux serializable values?

Redux (and Redux Toolkit's default middleware) expects state and actions to contain only plain, serializable data: strings, numbers, booleans, null, plain objects, and arrays. Values like class instances, Promises, functions, Map/Set, Symbol, or DOM elements are not serializable and shouldn't be put in the store or dispatched inside an action.

     // BAD: Date and a function are not serializable
     dispatch({
       type: "user/loaded",
       payload: { createdAt: new Date(), onDone: () => {} },
     });

     // GOOD: store a serializable representation instead
     dispatch({
       type: "user/loaded",
       payload: { createdAt: new Date().toISOString() },
     });
     

This matters because:

• Redux DevTools rely on serializing actions/state for time-travel debugging and persisting/replaying action logs.
• redux-persist needs to serialize state to localStorage/AsyncStorage.
• Non-serializable values can hide subtle bugs (e.g., mutable class instances bypassing Redux's change-detection).

Redux Toolkit's configureStore includes a serializableCheck middleware (dev-only) that warns in the console whenever a non-serializable value is dispatched or stored.