Redux Toolkit Tutorial - 4 - Three Principles

Redux Core Concepts
📌 The three core concepts in Redux are the store (holding application state), actions (describing what happened), and reducers (executing state transitions).
🍰 In the Cake Shop example, the store holds the count of cakes on the shelf.
⚡ Actions are simple objects, requiring a `type` property (e.g., `"cake_ordered"`) to describe the event.

Three Principles of Redux
1️⃣ The global state of the application must be stored as a single object inside the Redux store.
2️⃣ The only way to change the state is by dispatching an action; direct modification of the state object is prohibited (state is read-only).
3️⃣ State transformation is handled by writing pure reducers that take the previous state and an action as input and return the next state.

Reducer Functionality
⚙️ Pure reducers are pure functions that calculate the new state based on inputs without mutating the previous state, ensuring predictable behavior.
🛒 For the Cake Shop, the reducer acts like the shopkeeper: receiving an order (`action`), reducing the cake count by one, and returning the new count (new state).
🔄 For a given state and action (e.g., count $X$ and action "cake\_ordered"), the reducer will always return the same result ($X-1$).

Redux Flow Visualization
🔄 The application is subscribed to the Redux store but cannot update the state directly.
📩 State updates are triggered by dispatching an action.
👨‍💻 The reducer handles the dispatched action, updates the current state, and the new state value is automatically passed back to the subscribed application.

Key Points & Insights
➡️ Understand the separation of concerns: Store holds data, Actions describe events, Reducers manage state change logic.
➡️ Embrace immutability: Reducers must return a new state object rather than modifying the previous one.
➡️ The pattern involves: App $\rightarrow$ Dispatch Action $\rightarrow$ Reducer updates Store $\rightarrow$ App reflects New State.

📸 Video summarized with SummaryTube.com on Jan 19, 2026, 17:16 UTC