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Redux 的 store 是什么

React 进阶面试题, Redux 的 store 是什么?

React 进阶面试题, Redux 的 store 是什么?

QA

Step 1

Q:: What is Redux's store?

A:: Redux's store is a single JavaScript object that holds the entire state of an application. It is the central hub where all the application's state is kept, making it easier to manage and maintain the state across the application. The store is created using the createStore function and can only be updated by dispatching actions, ensuring a predictable flow of data.

Step 2

Q:: How does Redux's store work in an application?

A:: Redux's store works by holding the state of the application in a single, immutable data structure. Whenever an action is dispatched, the store's state is updated by a reducer function, which takes the current state and the action as input and returns a new state. This updated state is then available throughout the application via connected components, ensuring consistency across the app.

Step 3

Q:: Why is the store in Redux considered 'single source of truth'?

A:: In Redux, the store is considered the 'single source of truth' because it holds all the application state in one centralized place. This ensures that all components in the application have access to the same state and that state changes are predictable and traceable. This approach helps in debugging and scaling large applications.

Step 4

Q:: What are the benefits of using Redux's store in an application?

A:: The benefits of using Redux's store include: (1) Centralized state management, which makes the state predictable and easier to debug, (2) Improved scalability by having a single source of truth, (3) Ease of testing by isolating state management, and (4) Better maintainability as the application grows in complexity.

Step 5

Q:: Can you explain the process of updating the state in a Redux store?

A:: To update the state in a Redux store, an action must be dispatched. An action is a plain JavaScript object that describes a change in the application. The reducer function then handles this action and returns a new state based on the action's type and payload. The Redux store then replaces the current state with this new state, triggering re-renders in the connected components.

Step 6

Q:: How does Redux store integrate with React components?

A:: Redux integrates with React components through the react-redux library, which provides the Provider and connect functions. The Provider component wraps the root component of the app, making the Redux store available to all components. The connect function is used to connect individual components to the store, allowing them to access state and dispatch actions as props.

用途

Interviewing candidates on Redux`'s store is crucial because it is fundamental to managing state in a predictable and maintainable way in React applications, especially as they scale. Understanding how to use Redux's store is essential for building large, complex applications where state management needs to be consistent and traceable. In a production environment, Redux is used when there is a need for complex state management, such as when multiple components need to share and synchronize state or when the application has a large number of state transitions.`\n

相关问题

🦆
What is a reducer in Redux?▷

A reducer is a pure function in Redux that takes the current state and an action as input and returns a new state. It determines how the state of the application changes in response to an action by checking the action type and updating the state accordingly.

🦆
What are actions in Redux and how are they used?▷

Actions in Redux are plain JavaScript objects that describe what happened in the application. They typically have a type field that indicates the action's purpose, and they may include additional data (payload) needed to update the state. Actions are dispatched to the store to trigger state changes.

🦆
How do you manage side effects in Redux?▷

Side effects in Redux are managed using middleware such as redux-thunk or redux-saga``. These middlewares allow for asynchronous actions (e.g., API calls) to be handled separately from the reducers, ensuring that the state management remains pure and predictable.

🦆
What are selectors in Redux and why are they important?▷

Selectors are functions that extract specific pieces of state from the Redux store. They are important because they encapsulate the logic for retrieving state, making the components more decoupled from the state structure, improving maintainability and testability.

🦆
What are some best practices for structuring a Redux store in a large application?▷

Best practices for structuring a Redux store in a large application include (1) splitting reducers by domain using combineReducers``, (2) normalizing state to avoid nested structures, (3) using selectors to encapsulate state access, (4) keeping actions and reducers together in feature folders, and (5) avoiding unnecessary re-renders by using shouldComponentUpdate or memoization techniques.

React 状态管理面试题, Redux 的 store 是什么?

QA

Step 1

Q:: Redux 的 store 是什么？

A:: Redux 的 store 是整个应用程序的状态存储的地方。Store 是一个 JavaScript 对象，它包含了应用的所有状态数据，并且只有通过 dispatch action 才能更新 store 中的状态。Store 负责管理应用的状态树，并提供 getState() 方法来访问当前的状态。它还允许注册订阅者，当状态发生变化时，订阅者会被通知。

Step 2

Q:: 如何在 Redux 中创建一个 store？

A:: 要在 Redux 中创建一个 store，需要使用 Redux 提供的 createStore 函数。通常情况下，会将一个 root reducer 作为参数传递给 createStore 函数来初始化 store。还可以传递中间件（如 applyMiddleware）来增强 store 的功能。

 
import { createStore } from 'redux';
import rootReducer from './reducers';
 
const store = createStore(rootReducer);

此外，开发环境中通常会使用 redux-devtools-extension 来方便调试。

Step 3

Q:: Redux 中的 action 是什么？

A:: Redux 中的 action 是一个描述事件的普通 JavaScript 对象。它是 store 数据唯一的来源，action 对象必须有一个 type 字段，表示要执行的动作类型。除此之外，可以添加任何其他字段来传递额外的信息。

 
const action = {
  type: 'ADD_TODO',
  payload: { text: 'Learn Redux' }
};

Step 4

Q:: 什么是 Redux 中的 reducer？

A:: Reducer 是一个纯函数，它接收两个参数：当前的状态（state）和一个 action，并返回一个新的状态。Reducer 根据 action 的类型来决定如何更新状态。Reducer 不应直接修改 state，而是返回一个新的 state 对象。

 
const initialState = { count: 0 };
 
function counterReducer(state = initialState, action) {
  switch (action.type) {
    case 'INCREMENT':
      return { ...state, count: state.count + 1 };
    case 'DECREMENT':
      return { ...state, count: state.count - 1 };
    default:
      return state;
  }
}

Step 5

Q:: 为什么 Redux 需要中间件（middleware）？

A:: Redux 的中间件允许在 action 被发送到 reducer 之前对其进行处理。它们可以用于记录日志、处理异步操作（如 redux-thunk 或 redux-saga）、调用 API、捕获错误等。中间件提供了在 action 和 reducer 之间执行自定义逻辑的能力，增强了 Redux 的灵活性和可扩展性。

 
const logger = store => next => action => {
  console.log('dispatching', action);
  let result = next(action);
  console.log('next state', store.getState());
  return result;
};
 
const store = createStore(rootReducer, applyMiddleware(logger));

Step 6

Q:: Redux 如何处理异步操作？

A:: Redux 本身是同步的，但可以通过中间件处理异步操作。最常用的异步中间件是 redux-thunk 和 redux-saga。

- redux-thunk 允许 action creators 返回一个函数而不是 action 对象，这个函数可以执行异步代码并在合适的时机 dispatch 一个 action。

 
const fetchUserData = () => {
  return async dispatch => {
    dispatch({ type: 'FETCH_USER_REQUEST' });
    try {
      const response = await fetch('/api/user');
      const data = await response.json();
      dispatch({ type: 'FETCH_USER_SUCCESS', payload: data });
    } catch (error) {
      dispatch({ type: 'FETCH_USER_FAILURE', error });
    }
  };
};

- redux-saga 通过使用 generator 函数来处理复杂的异步操作，可以在 action 发出后以声明性的方式执行异步任务。

Step 7

Q:: Redux 的三大原则是什么？

A:: Redux 的三大原则是：

1. 单一数据源：整个应用的状态存储在一个单一的 store 对象中，单一的状态树使得调试和检查状态变得更简单。 2. 状态是只读的：唯一改变状态的方法是触发 action，action 是一个描述已发生事件的对象。 3. 使用纯函数来执行修改：Reducer 负责描述状态如何变化，是纯函数，这意味着给定相同的输入（当前状态和 action），它总是会返回相同的输出（新的状态）。

用途

这些问题通常会在面试中出现，因为 Redux 是 React 应用中管理全局状态的常用工具。面试官想通过这些问题了解候选人对 Redux 核心概念的掌握情况，包括 store、action、reducer 等。Redux 特别适用于那些需要在多个组件间共享状态、处理复杂状态逻辑、或需要在状态变化时触发大量副作用的应用。了解 Redux 的工作原理对构建可维护、可预测的大型 React 应用至关重要。\n

相关问题

🦆
React 如何实现状态管理?▷

React 通过 useState 和 useReducer 等 Hook 来管理组件内部的状态。对于全局状态，可以使用 Context API 或第三方库如 Redux、MobX、Recoil 等。

🦆
如何优化 Redux 中的性能?▷

可以通过使用 reselect 库来创建 memoized 选择器，避免不必要的重新计算；使用 React.memo 或 shouldComponentUpdate 来避免不必要的重新渲染；合理地拆分 reducer 和 action 以减少复杂度。

🦆
Redux 和 MobX 的区别是什么?▷

Redux 强调不可变数据和纯函数，具有较高的可预测性和调试性，而 MobX 是响应式的，使用 observable 来自动追踪依赖并更新状态，代码更为简洁但不如 Redux 可预测。

🦆
如何在 Redux 中处理大型应用的状态管理?▷

可以通过拆分 reducer、使用 combineReducers 组织不同领域的状态、使用 redux-toolkit 简化 Redux 逻辑、使用动态加载 reducer 等方式来管理大型应用的状态。

🦆
Redux 与 React Context API 的对比▷

Redux 适合处理复杂的状态逻辑和需要严格状态管理的场景，而 Context API 适合轻量级的状态共享和避免 prop drilling 的场景。Context API 通常搭配 useReducer 使用来实现类似 Redux 的功能。

Redux当 React 的多个组件有自己的 state同时需要维护一些公共状态时该如何设计和管理这些状态