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Showing of 93What are the three core principles of Redux?
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- Single source of truth: The global state is stored in a single store
- State is read-only: State can only be changed by dispatching actions
- Changes are made with pure functions: Reducers are pure functions that specify how state changes in response to actions
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What is a Redux store?
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The Redux store is a single JavaScript object that holds the complete state tree of your application. It provides methods to:
getState(): Returns current statedispatch(action): Dispatches an action to trigger state changesubscribe(listener): Registers a listener function
import { createStore } from 'redux';
const store = createStore(reducer);
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What are actions in Redux?
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Actions are plain JavaScript objects that describe what happened in the application. They must have a type property and can contain additional data (payload).
// Action object
const addTodo = {
type: 'ADD_TODO',
payload: {
id: 1,
text: 'Learn Redux'
}
};
// Action creator function
const addTodoAction = (text) => ({
type: 'ADD_TODO',
payload: { id: Date.now(), text }
});
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What are reducers in Redux?
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Reducers are pure functions that take the current state and an action, and return a new state. They specify how the application's state changes in response to actions.
const todosReducer = (state = [], action) => {
switch (action.type) {
case 'ADD_TODO':
return [...state, action.payload];
case 'REMOVE_TODO':
return state.filter(todo => todo.id !== action.payload.id);
default:
return state;
}
};
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What is the difference between actions and action creators?
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- Actions: Plain JavaScript objects with a
typeproperty - Action creators: Functions that return action objects
// Action
const action = { type: 'INCREMENT', payload: 1 };
// Action creator
const increment = (value) => ({
type: 'INCREMENT',
payload: value
});
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How do you connect React components to Redux store?
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Using React-Redux library:
- Wrap app with
Providercomponent - Use
useSelectorhook to read state - Use
useDispatchhook to dispatch actions
// App.js
import { Provider } from 'react-redux';
<Provider store={store}>
<App />
</Provider>
// Component
import { useSelector, useDispatch } from 'react-redux';
const todos = useSelector(state => state.todos);
const dispatch = useDispatch();
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What is the purpose of the Provider component in React-Redux?
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The Provider component makes the Redux store available to all nested components. It uses React's context API to pass the store down the component tree without manual prop passing.
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What is dispatching in Redux?
Why should reducers be pure functions?
How does Redux Toolkit differ from traditional Redux?
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Key differences include:
- Less boilerplate: RTK eliminates action creators, action types, and switch statements
- Immer integration: Allows "mutative" logic that's actually immutable under the hood
- Built-in middleware: Includes redux-thunk and other middleware by default
- DevTools: Automatically configured Redux DevTools
- TypeScript support: Better TypeScript integration out of the box
- Modern patterns: Encourages modern Redux patterns and best practices
Traditional Redux required separate action creators, reducers with switch statements, and manual store configuration. RTK consolidates these into simpler APIs.
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What is `configureStore` and what advantages does it provide?
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configureStore is RTK's enhanced version of Redux's createStore. It provides several advantages:
- Automatic middleware setup: Includes redux-thunk and development-time middleware
- DevTools integration: Automatically connects to Redux DevTools
- Serializable state checks: Warns about non-serializable values in development
- Immutability checks: Detects state mutations in development
- Simplified configuration: Reduces boilerplate for common store setup
const store = configureStore({
reducer: {
counter: counterSlice.reducer,
user: userSlice.reducer
}
});
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Explain the concept of "slices" in Redux Toolkit
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A slice is a collection of Redux reducer logic and actions for a single feature of your application. It's created using createSlice and includes:
- Initial state: The starting value for this slice of state
- Reducers: Functions that define how state updates in response to actions
- Actions: Automatically generated action creators based on reducer names
- Action types: Automatically generated action type strings
Slices eliminate the need to write separate action creators and action types, reducing boilerplate significantly.
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What is Redux middleware and how does it work?
What is Redux Thunk and when would you use it?
What is Redux Toolkit (RTK) and why should you use it?
What is the difference between mapStateToProps and useSelector?
How do you handle asynchronous actions in Redux?
What are selectors in Redux and why are they important?
What is the difference between Redux and Context API?
How do you combine multiple reducers in Redux?
What is the purpose of Redux DevTools?
How do you test Redux reducers?
What is createSlice in Redux Toolkit?
What is the difference between Redux and MobX?
How do you handle form state in Redux?
What is createAsyncThunk in Redux Toolkit?
How do you prevent unnecessary re-renders in Redux?
How does `createSlice` work and what does it return?
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createSlice accepts a configuration object and returns an object containing:
- reducer: The slice reducer function
- actions: Object with action creators for each reducer
- name: The slice name
- getInitialState: Function returning initial state
const counterSlice = createSlice({
name: 'counter',
initialState: { value: 0 },
reducers: {
increment: (state) => {
state.value += 1; // Immer makes this safe
},
incrementByAmount: (state, action) => {
state.value += action.payload;
}
}
});
// Returns: { reducer, actions: { increment, incrementByAmount } }
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How does Immer integration work in Redux Toolkit?
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RTK uses Immer under the hood, allowing you to write "mutative" logic that's actually immutable:
- Direct mutations: You can modify state directly in reducers
- Immer magic: Immer creates a new immutable state tree
- Performance: Immer optimizes updates by only changing what's necessary
- Type safety: Works seamlessly with TypeScript
You can either mutate the draft state OR return a new state, but not both in the same reducer.
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What are `extraReducers` and when would you use them?
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extraReducers allow a slice to respond to actions that weren't defined in its own reducers field:
- External actions: Handle actions from other slices
- Async thunks: Handle pending/fulfilled/rejected states from
createAsyncThunk - Action matching: Use builder pattern or map object notation
const userSlice = createSlice({
name: 'user',
initialState: { data: null, loading: false },
reducers: {},
extraReducers: (builder) => {
builder
.addCase(fetchUser.pending, (state) => {
state.loading = true;
})
.addCase(fetchUser.fulfilled, (state, action) => {
state.data = action.payload;
state.loading = false;
});
}
});
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How do you handle complex state updates with nested objects in RTK?
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Thanks to Immer, you can directly modify nested properties:
const userSlice = createSlice({
name: 'user',
initialState: {
profile: {
name: '',
address: {
street: '',
city: ''
}
}
},
reducers: {
updateAddress: (state, action) => {
// Direct assignment works with Immer
state.profile.address = action.payload;
},
updateCity: (state, action) => {
state.profile.address.city = action.payload;
}
}
});
For complex scenarios, you might still return a new state object if the logic is clearer that way.
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What is the `prepare` callback in RTK reducers?
What is `createAsyncThunk` and how does it work?
How do you handle loading states with `createAsyncThunk`?
What are the options available in `createAsyncThunk`'s `thunkAPI` parameter?
What is RTK Query and how does it differ from createAsyncThunk?
How do you define an API service with RTK Query?
How do you optimize component re-renders when using Redux Toolkit?
How do you test Redux Toolkit slices and async thunks?
What are RTK Query hooks and how do they work?
How do you handle RTK Query conditional fetching?
How do you handle RTK Query error scenarios?
How do you implement pagination with RTK Query?
How do you handle file uploads with RTK Query?
Explain Redux middleware composition and how it works internally
How would you implement undo/redo functionality in Redux?
What are the performance implications of Redux and how do you optimize them?
How do you implement middleware for API calls with caching?
Explain the concept of Redux state normalization and its benefits
How would you implement optimistic updates in Redux?
What is the difference between Redux Saga and Redux Thunk?
How do you handle complex state updates with Immer in Redux Toolkit?
How would you implement a Redux store enhancer?
What are higher-order reducers and when would you use them?
How do you implement real-time updates with Redux?
How would you implement feature flags in Redux?
What are some advanced patterns for code splitting with Redux?
How do you handle side effects testing in Redux applications?
How would you implement a time-travel debugging feature?
What are the best practices for organizing Redux code in large applications?
How do you implement custom equality checks for useSelector?
How would you implement state persistence with encryption?
How do you handle concurrent actions and race conditions in Redux?
What strategies would you use for Redux performance monitoring and debugging?
How would you implement a Redux-based state machine?
How do you implement Redux patterns with modern React Server Components?
What are modern Redux patterns for handling authentication and authorization?
How do you handle complex async workflows with Redux?
What are the best practices for Redux in large-scale applications?
How do you handle race conditions and request cancellation with RTK?
How does caching work in RTK Query?
What are cache tags and how do you use them for cache invalidation?
How do you handle optimistic updates with RTK Query?
How do you implement custom base queries in RTK Query?
What are entity adapters and when should you use them?
How do you structure large Redux applications with RTK?
How do you handle side effects and middleware with RTK?
How do you handle data normalization patterns with RTK?
How do you implement middleware for logging and debugging in RTK?
How do you handle code splitting and lazy loading of Redux slices?
How do you implement custom RTK Query transformations?
How do you implement RTK Query with authentication?
How do you implement RTK Query batch operations?
How do you implement RTK Query with WebSocket streaming?
How do you test RTK Query endpoints?
How do you implement RTK Query cache invalidation strategies?
How do you handle optimistic updates with conflict resolution?
How do you implement RTK Query with TypeScript generics?
How do you implement custom cache selectors with RTK Query?
How do you implement RTK Query with complex caching strategies?
How do you implement RTK Query monitoring and analytics?
How do you implement data synchronization patterns with RTK Query?
How do you implement comprehensive performance optimization for RTK Query?
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Redux cheatsheet
- Core Concepts01
- Basic Building Blocks02
- Redux Toolkit (Modern Redux)03
- React-Redux Integration04
- Middleware05
- Async Operations06
- Performance Optimization07
- Best Practices08
- Key Interview Concepts09
- Testing Redux10
- RTK Query (Data Fetching)11
- Advanced Patterns12
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