State Reducer Pattern in react.
Published: 2024-01-07 16:34:43

---
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**Understanding the State Reducer Pattern**
The State Reducer Pattern is a powerful technique.
State Reducer Pattern is the concept of "state reducers." These are functions
responsible for handling state transitions based on actions dispatched to them.
The pattern fosters a unidirectional flow of data, making it easier to reason
about the application's state changes.
Advantages of the State Reducer Pattern
The State Reducer Pattern offers several advantages including:
1. Improved Separation of Concerns:
By encapsulating state logic within reducers, the component's
responsibilities become clearer, leading to better maintainability.
2. Reusability:
Reducers can be reused across components, leading to a more modular
and organized codebase.
3. Predictable State Changes:
As reducers follow strict patterns, it becomes easier to predict and test
state transitions, reducing bugs and unexpected behavior.
Implementing the State Reducer Pattern
Now, let's walk through a step-by-step guide on how to implement the State
Reducer Pattern in a React application using React Hooks:

```
import { useState } from 'react';
const App = () => {
const initialState = {
count: 0,
isLoading: false,
};
const [state, setState] = useState(initialState);
const reducer = (state, action) => {
switch (action.type) {
case 'INCREMENT':
return { ...state, count: state.count + 1 };

case 'DECREMENT':
return { ...state, count: state.count - 1 };
case 'SET_LOADING':
return { ...state, isLoading: action.payload };
default:
return state;
}
}
const dispatch = (action) => {
const newState = reducer(state, action);
setState(newState);
}
const handleIncrement = () => {
dispatch({ type: 'INCREMENT' });
};
}
export default App;
```

Step 1: Setting up the State
In your functional component, start by declaring the initial state using the
useState hook.
Step 2: Creating the Reducer
Next, define your reducer function responsible for handling state changes
based on dispatched actions. The reducer function takes the current state and
an action object as arguments and returns the new state:
Step 3: Dispatching Actions
In your component, you can dispatch actions using regular function calls. Each
action will be processed by the reducer, and the state will be updated
accordingly.

## State reducer pattern with
zustand.

If you can't live without Redux-like reducers, you can define a dispatch function
on the root level of
the store.
for example:

```
export const useCartStore = create<CartStore>((set) => ({
/* other state properties... */
dispatch: (action: Action) => set((state) => reducer(state,
action)),
}));
import {create} from 'zustand'
//TypeScript interfaces has been omitted for simplicity.
const actions: Actions= {
addToCart: (state: CartStore, action: Action) => {
const { id } = action.payload;
const index = state.cart.findIndex((item) => item.id === id);
if (index >= 0) {
const cart = [
...state.cart.slice(0, index),
{ ...state.cart[index], quantity:
state.cart[index].quantity + 1 },
...state.cart.slice(index + 1),
];
const newState = {
...state,
cart,
};
updateLocalStorage(newState);
return newState;
}
//action.payload refers to the "product".
const cart = [...state.cart, { ...action.payload, quantity: 1
}];
const newState = { ...state, cart };
updateLocalStorage(newState);
return newState;
},
removeFromCart: (state: CartStore, action: Action) => {
const { id } = action.payload;
const newState = {...state, cart:state.cart.filter((item) =>
item.id !== id)};
updateLocalStorage(newState);
return newState;
},
emptyCart: () => {
updateLocalStorage([]);
return [];
},
};
const reducer = (state: CartStore, action: Action) => {
const { type } = action;
const currentAction = actions[type];
return currentAction ? currentAction(state, action) : state;
};
export const useCartStore = create<CartStore>((set) => ({
cart: [],
product: {},
dispatch: (action: Action) => set((state) => reducer(state,
action)),
}));

/*example of how to consume the store
import {useCartStore} from 'store'
const cart = useCartStore( state => state.cart )
const product = useCartStore( state => state.product )
const dispatch = useCartStore((state) => state.dispatch)
dispatch({type:'addItemToCart', payload: product})
*/

```
It will continue...