Redux slices and actions in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Redux slice with a name.

React Native

import { createSlice } from '@reduxjs/toolkit';

const counterSlice = createSlice({
  name: '[1]',
  initialState: 0,
  reducers: {}
});

Drag options to blanks, or click blank then click option'

Acounter

Baction

Cstate

Dstore

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'store' or 'state' as the slice name, which are not descriptive slice names.

Leaving the name empty or undefined.

The name property defines the slice name, which is usually descriptive like 'counter'.

2fill in blank

medium

Complete the code to add a reducer that increments the state by 1.

React Native

const counterSlice = createSlice({
  name: 'counter',
  initialState: 0,
  reducers: {
    increment: (state) => state [1] 1
  }
});

Drag options to blanks, or click blank then click option'

A-

B+=

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' inside the reducer return statement, which is invalid here.

Using '-' or '*' which changes the state incorrectly.

The reducer returns the new state by adding 1 to the current state using the '+' operator.

3fill in blank

hard

Fix the error in the reducer to correctly update the state by incrementing it.

React Native

const counterSlice = createSlice({
  name: 'counter',
  initialState: 0,
  reducers: {
    increment: (state) => {
      state [1] 1;
    }
  }
});

Drag options to blanks, or click blank then click option'

A+=

B+

C-=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' operator alone without assignment.

Using '-=' or '*=' which changes state incorrectly.

When using Immer in Redux Toolkit, you can mutate the state directly with state += 1;. The correct syntax is state += 1;.

4fill in blank

hard

Fill both blanks to export the action and reducer from the slice.

React Native

export const { [1] } = counterSlice.actions;
export default counterSlice.[2];

Drag options to blanks, or click blank then click option'

Aincrement

Bactions

Creducer

Dreducers

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'actions' instead of the specific action name.

Exporting 'reducers' instead of 'reducer'.

The action increment is exported from counterSlice.actions. The default export is the reducer property.

5fill in blank

hard

Fill all three blanks to create a Redux store with the counter reducer.

React Native

import { configureStore } from '@reduxjs/toolkit';
import counterReducer from './counterSlice';

const store = configureStore({
  reducer: {
    [1]: [2]
  }
});

export default [3];

Drag options to blanks, or click blank then click option'

Acounter

BcounterReducer

Cstore

Dreducer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reducer' as the key instead of the slice name.

Exporting something other than the store.

The store is configured with a reducer object where the key is the slice name counter and the value is the imported counterReducer. The store is exported as default.

Practice

1. What is the main purpose of a Redux slice in a React Native app?

easy

A. To create UI components automatically

B. To style the app with CSS

C. To handle navigation between screens

D. To group related state and actions together for easier management

Solution

1. Step 1: Understand Redux slice role

   A slice groups state and actions related to a feature in one place.

2. Step 2: Compare with other options

   Options A, C, and D are unrelated to state management.

3. Final Answer:

   To group related state and actions together for easier management -> Option D

4. Quick Check:

   Redux slice = group state and actions [OK]

Hint: Slices bundle state and actions for one feature [OK]

Common Mistakes:

• Confusing slices with UI components
• Thinking slices handle navigation
• Assuming slices style the app

2. Which of the following is the correct way to define an action inside a Redux slice using createSlice?

easy

A. reducers: { increment: (state) => { state.value += 1 } }

B. actions: { increment: () => state.value += 1 }

C. reducers: { increment: () => state.value += 1 }

D. actions: { increment: (state) => { return state.value + 1 } }

Solution

1. Step 1: Recall createSlice syntax

   Reducers are defined as functions with (state) parameter that mutate state directly.

2. Step 2: Check each option

   reducers: { increment: (state) => { state.value += 1 } } correctly uses reducers with state mutation. Options B and D wrongly use 'actions' key. reducers: { increment: () => state.value += 1 } uses arrow function without braces, which won't mutate state properly.

3. Final Answer:

   reducers: { increment: (state) => { state.value += 1 } } -> Option A

4. Quick Check:

   Reducers mutate state inside createSlice [OK]

Hint: Reducers mutate state; actions key is not used in createSlice [OK]

Common Mistakes:

• Using 'actions' instead of 'reducers' key
• Not mutating state directly inside reducer
• Returning new state instead of mutating

3. Given this slice code:

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {
    increment: (state) => { state.value += 1 },
    decrement: (state) => { state.value -= 1 }
  }
});

const state = { value: 5 };
counterSlice.reducer(state, { type: 'counter/increment' });
console.log(state.value);

What will be logged to the console?

medium

A. 6

B. 5

C. NaN

D. Error

Solution

1. Step 1: Understand reducer call

   The reducer receives state { value: 5 } and action type 'counter/increment'. It runs increment reducer which adds 1 to state.value.

2. Step 2: Calculate new state value

   5 + 1 = 6, so state.value becomes 6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Increment action adds 1 to value [OK]

Hint: Reducer mutates state.value by +1 on increment action [OK]

Common Mistakes:

• Thinking state is immutable and unchanged
• Confusing action type format
• Expecting error due to direct mutation

4. You wrote this slice but dispatching the action does not update the state:

const todoSlice = createSlice({
  name: 'todo',
  initialState: [],
  reducers: {
    addTodo: (state, action) => {
      state.push(action.payload);
    }
  }
});

// Later in component
dispatch(todoSlice.actions.addTodo('Buy milk'));

What is the most likely reason the UI does not update?

medium

A. The reducer mutates state directly which is not allowed

B. The initialState should be an object, not an array

C. The slice reducer is not added to the store

D. The action payload is missing

Solution

1. Step 1: Check reducer code

   The reducer correctly mutates state array by pushing new todo, which is allowed with Immer in createSlice.

2. Step 2: Identify missing integration

   If UI does not update, likely the slice reducer is not connected to the Redux store, so dispatch has no effect.

3. Final Answer:

   The slice reducer is not added to the store -> Option C

4. Quick Check:

   Reducer must be in store for dispatch to update state [OK]

Hint: Always add slice reducer to store for updates [OK]

Common Mistakes:

• Thinking direct mutation is forbidden in createSlice
• Assuming initialState must be object
• Forgetting to add reducer to store

5. You want to create a Redux slice that manages a list of users and includes an action to update a user's name by id. Which code snippet correctly implements this?

hard

A. reducers: { updateName: (state, action) => { state.filter(u => u.id !== action.payload.id).push(action.payload); } }

B. reducers: { updateName: (state, action) => { const user = state.find(u => u.id === action.payload.id); if(user) { user.name = action.payload.name; } } }

C. reducers: { updateName: (state, action) => { state = state.map(u => u.id === action.payload.id ? { ...u, name: action.payload.name } : u); } }

D. reducers: { updateName: (state, action) => { state.map(u => u.id === action.payload.id ? { ...u, name: action.payload.name } : u); } }

Solution

1. Step 1: Understand mutation in createSlice

   Reducers can mutate state directly because Immer handles immutability internally.

2. Step 2: Analyze each option

   reducers: { updateName: (state, action) => { const user = state.find(u => u.id === action.payload.id); if(user) { user.name = action.payload.name; } } } finds user by id and mutates name directly, which is correct. reducers: { updateName: (state, action) => { state.map(u => u.id === action.payload.id ? { ...u, name: action.payload.name } : u); } } executes map but discards the new array without returning it or mutating state, incorrect. reducers: { updateName: (state, action) => { state = state.map(u => u.id === action.payload.id ? { ...u, name: action.payload.name } : u); } } tries to assign new array to state variable, which does not update state correctly. reducers: { updateName: (state, action) => { state.filter(u => u.id !== action.payload.id).push(action.payload); } } filters out user and pushes new one, which mutates array incorrectly and may cause bugs.

3. Final Answer:

   reducers: { updateName: (state, action) => { const user = state.find(u => u.id === action.payload.id); if(user) { user.name = action.payload.name; } } } -> Option B

4. Quick Check:

   Direct mutation with find and update is correct in createSlice [OK]

Hint: Use find and mutate user directly inside reducer [OK]

Common Mistakes:

• Trying to reassign state variable inside reducer
• Using filter and push incorrectly
• Not mutating state directly in createSlice