What is the difference between an immutable update and a mutable update?

Difficulty: 6/10

Redux Toolkit, Immer, State Mutability

Difference Between Immutable and Mutable Updates in Redux Toolkit

In Redux, state must always be treated as immutable — meaning you never modify existing objects or arrays directly. Instead, you create new copies with the updated data. Redux Toolkit uses Immer to simplify this process by allowing code that looks 'mutable' while still producing immutable updates.

Key Differences

1
Mutable Update: Directly changes the original object or array in memory (e.g., state.value += 1).
2
Immutable Update: Creates a new copy of the state with the updated values, leaving the original unchanged.
3
Redux Toolkit uses Immer to automatically convert apparent 'mutations' into immutable updates.
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This ensures state integrity while keeping reducer code concise and intuitive.

Example: Immutable vs Mutable Updates

So while mutable updates directly alter data, immutable updates produce new state objects. Redux Toolkit abstracts this complexity through Immer, ensuring reducers stay pure and predictable.

Scenario Questions

0-2 years experience

Follow-up Questions