面向开发人员的综合 React.js 备忘单

React.js 已成为现代 Web 开发中构建动态和高性能 Web 应用程序的基石。这份全面的备忘单将涵盖您掌握 React.js 所需了解的所有内容，包括实际示例、代码片段以及所有功能的详细说明。我们的目标是提供您可以随时参考的深入指南。

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1.React简介

React.js，通常简称为 React，是一个开源 JavaScript 库，用于构建用户界面，特别是对于需要快速、交互式用户体验的单页应用程序。 React 由 Facebook 开发，允许开发人员创建大型 Web 应用程序，这些应用程序可以有效地更新和渲染以响应数据更改。

React 的核心概念是组件，它是一个独立的模块，用于呈现一些输出。组件可以独立嵌套、管理和处理，使开发过程高效且可维护。

2. React 入门

设置环境

在开始使用React之前，您需要设置开发环境。方法如下：

1. 安装 Node.js 和 npm：React 依赖 Node.js 和 npm（Node Package Manager）来管理依赖项。

• 从官网下载并安装Node.js。

• 通过运行验证安装：
  

   node -v
   npm -v
  

1. 安装 Create React App：Create React App 是学习 React 的舒适环境，也是在 React 中启动新的单页应用程序的好方法。
   

   npm install -g create-react-app
   

创建一个新的 React 应用程序

环境设置完成后，您就可以创建新的 React 应用程序。

1. 创建一个新项目：
   

   npx create-react-app my-app
   cd my-app
   npm start
   

此命令创建一个具有指定名称（my-app）的新目录，设置一个新的 React 项目，并启动开发服务器。您可以打开浏览器并访问 http://localhost:3000 来查看新的 React 应用程序。

3. 反应组件

组件是任何 React 应用程序的构建块。它们让您可以将 UI 分成独立的、可重用的部分。

功能组件

函数式组件是接受 props 作为参数并返回 React 元素的 JavaScript 函数。它们比类组件更简单、更容易编写。

import React from 'react';

const Welcome = ({ name }) => {
  return 4a249f0d628e2318394fd9b75b4636b1Welcome, {name}!473f0a7621bec819994bb5020d29372a;
};

export default Welcome;

类组件

类组件是扩展 React.Component 的 ES6 类，并具有返回 React 元素的 render 方法。

import React, { Component } from 'react';

class Welcome extends Component {
  render() {
    return 4a249f0d628e2318394fd9b75b4636b1Welcome, {this.props.name}!473f0a7621bec819994bb5020d29372a;
  }
}

export default Welcome;

功能组件和类组件之间的差异

• 状态管理：函数式组件使用钩子（useState、useEffect等）进行状态管理，而类组件使用this.state和生命周期方法。

• 生命周期方法：类组件具有生命周期方法，例如 componentDidMount、componentDidUpdate 和 componentWillUnmount。功能组件使用 useEffect 钩子来处理副作用。

• 简单性：函数式组件更简单、更简洁，使它们更易于阅读和维护。

4.JSX

JSX 是一个语法扩展，允许您直接在 JavaScript 中编写 HTML。它产生 React“元素”。

JSX 语法

JSX 看起来像 HTML，但被转换为 JavaScript。

const element = 4a249f0d628e2318394fd9b75b4636b1Hello, world!473f0a7621bec819994bb5020d29372a;

嵌入表达式

您可以通过将任何 JavaScript 表达式括在大括号中来将其嵌入到 JSX 中。

const name = 'John';
const element = 4a249f0d628e2318394fd9b75b4636b1Hello, {name}!473f0a7621bec819994bb5020d29372a;

JSX 属性

JSX 允许您使用类似于 HTML 语法的属性。

const element = 475c150c326c59ec9b2dd1e6a1c38014;

5. 状态和道具

了解状态

State 是一个内置对象，用于存储属于组件的属性值。当状态对象发生变化时，组件会重新渲染。

使用 useState Hook 管理状态

useState 钩子用于向功能组件添加状态。

import React, { useState } from 'react';

const Counter = () => {
  const [count, setCount] = useState(0);

  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      e388a4556c0f65e1904146cc1a846beeYou clicked {count} times94b3e26ee717c64999d7867364b1b4a3
      5ddc0978355752d4bf828563dc007a14 setCount(count + 1)}>Click me65281c5ac262bf6d81768915a4a77ac0
    16b28748ea4df4d9c2150843fecfba68
  );
};

export default Counter;

了解道具

Props 是传递给 React 组件的参数。 Props 通过 HTML 属性传递给组件。

传递道具

道具是只读且不可变的。

const Greeting = (props) => {
  return 4a249f0d628e2318394fd9b75b4636b1Hello, {props.name}!473f0a7621bec819994bb5020d29372a;
};

const App = () => {
  return 1e9b83e740a258dee7f01e880ba004db;
};

道具类型和默认道具

PropTypes 允许您定义组件应接收的 props 类型。可以定义默认 props 以确保 prop 在未指定的情况下具有值。

import React from 'react';
import PropTypes from 'prop-types';

const Greeting = ({ name }) => {
  return 4a249f0d628e2318394fd9b75b4636b1Hello, {name}!473f0a7621bec819994bb5020d29372a;
};

Greeting.propTypes = {
  name: PropTypes.string.isRequired,
};

Greeting.defaultProps = {
  name: 'Guest',
};

export default Greeting;

6. Component Lifecycle

Lifecycle Methods in Class Components

Lifecycle methods are special methods in class components that run at specific points in a component's life.

• componentDidMount: Executed after the component is rendered.

• componentDidUpdate: Executed after the component's updates are flushed to the DOM.

• componentWillUnmount: Executed before the component is removed from the DOM.
  

class MyComponent extends React.Component {
  componentDidMount() {
    // Runs after component is mounted
  }

  componentDidUpdate(prevProps, prevState) {
    // Runs after component updates
  }

  componentWillUnmount() {
    // Runs before component is unmounted
  }

  render() {
    return dc6dce4a544fdca2df29d5ac0ea9906bMy Component16b28748ea4df4d9c2150843fecfba68;
  }
}

Using useEffect Hook

The useEffect hook combines the functionalities of componentDidMount, componentDidUpdate, and componentWillUnmount.

import React, { useState, useEffect } from 'react';

const MyComponent = () => {
  const [count, setCount] = useState(0);

  useEffect(() => {
    // Runs on mount and update
    document.title = `You clicked ${count} times`;

    // Cleanup function (runs on unmount)
    return () => {
      console.log('Cleanup');
    };
  }, [count]); // Dependency array

  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      e388a4556c0f65e1904146cc1a846beeYou

 clicked {count} times94b3e26ee717c64999d7867364b1b4a3
      5ddc0978355752d4bf828563dc007a14 setCount(count + 1)}>Click me65281c5ac262bf6d81768915a4a77ac0
    16b28748ea4df4d9c2150843fecfba68
  );
};

export default MyComponent;

7. Handling Events

Event Handling in React

React events are named using camelCase, rather than lowercase. With JSX, you pass a function as the event handler, rather than a string.

const handleClick = () => {
  console.log('Button clicked');
};

const MyComponent = () => {
  return a2cfc4f771b7cbacb8fc705e23ded36bClick me65281c5ac262bf6d81768915a4a77ac0;
};

Synthetic Events

React's event system is known as Synthetic Events. It is a cross-browser wrapper around the browser's native event system.

Handling Forms

Handling forms in React involves controlling the input elements and managing the state.

import React, { useState } from 'react';

const MyForm = () => {
  const [value, setValue] = useState('');

  const handleChange = (event) => {
    setValue(event.target.value);
  };

  const handleSubmit = (event) => {
    event.preventDefault();
    alert('A name was submitted: ' + value);
  };

  return (
    a9bf9d9bedc9abd7dd4d836a79412b6a
      2e1cf0710519d5598b1f0f14c36ba674
        Name:
        504d17b0f6b03dc75f5b399918bed261
      8c1ecd4bb896b2264e0711597d40766c
      92e8cbd9feac6a729893ae422743759e
    f5a47148e367a6035fd7a2faa965022e
  );
};

export default MyForm;

Event Handler Best Practices

• Avoid inline event handlers: Define event handlers outside of the JSX for better readability and performance.

• Use Arrow Functions: Use arrow functions to avoid issues with this binding.

• Debounce Expensive Operations: Debounce expensive operations like API calls to avoid performance issues.

8. Conditional Rendering

if-else Statements

You can use JavaScript if-else statements inside the render method.

const MyComponent = ({ isLoggedIn }) => {
  if (isLoggedIn) {
    return 4a249f0d628e2318394fd9b75b4636b1Welcome back!473f0a7621bec819994bb5020d29372a;
  } else {
    return 4a249f0d628e2318394fd9b75b4636b1Please sign in.473f0a7621bec819994bb5020d29372a;
  }
};

Ternary Operators

Ternary operators are a concise way to perform conditional rendering.

const MyComponent = ({ isLoggedIn }) => {
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      {isLoggedIn ? 4a249f0d628e2318394fd9b75b4636b1Welcome back!473f0a7621bec819994bb5020d29372a : 4a249f0d628e2318394fd9b75b4636b1Please sign in.473f0a7621bec819994bb5020d29372a}
    16b28748ea4df4d9c2150843fecfba68
  );
};

Logical && Operator

You can use the logical && operator to include elements conditionally.

const MyComponent = ({ isLoggedIn }) => {
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      {isLoggedIn && 4a249f0d628e2318394fd9b75b4636b1Welcome back!473f0a7621bec819994bb5020d29372a}
    16b28748ea4df4d9c2150843fecfba68
  );
};

Inline If with Logical && Operator

Inline if with logical && operator allows you to conditionally include an element in the output.

const Mailbox = ({ unreadMessages }) => {
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      4a249f0d628e2318394fd9b75b4636b1Hello!473f0a7621bec819994bb5020d29372a
      {unreadMessages.length > 0 &&
        c1a436a314ed609750bd7c7d319db4da
          You have {unreadMessages.length} unread messages.
        2e9b454fa8428549ca2e64dfac4625cd
      }
    16b28748ea4df4d9c2150843fecfba68
  );
};

9. Lists and Keys

Rendering Lists

You can build collections of elements and include them in JSX using curly braces {}.

const numbers = [1, 2, 3, 4, 5];
const listItems = numbers.map((number) =>
  2e99a2afa389bfb220fcd51d65729993
    {number}
  bed06894275b65c1ab86501b08a632eb
);

const NumberList = () => {
  return (
    ff6d136ddc5fdfeffaf53ff6ee95f185{listItems}929d1f5ca49e04fdcb27f9465b944689
  );
};

Using Keys

Keys help React identify which items have changed, are added, or are removed. Keys should be given to the elements inside the array to give the elements a stable identity.

const NumberList = (props) => {
  const numbers = props.numbers;
  const listItems = numbers.map((number) =>
    2e99a2afa389bfb220fcd51d65729993
      {number}
    bed06894275b65c1ab86501b08a632eb
  );
  return (
    ff6d136ddc5fdfeffaf53ff6ee95f185{listItems}929d1f5ca49e04fdcb27f9465b944689
  );
};

Keys Must Only Be Unique Among Siblings

Keys used within arrays should be unique among their siblings.

function Blog(props) {
  const sidebar = (
    ff6d136ddc5fdfeffaf53ff6ee95f185
      {props.posts.map((post) =>
        87c6bb9020f9bc84ce365f117dbefb25
          {post.title}
        bed06894275b65c1ab86501b08a632eb
      )}
    929d1f5ca49e04fdcb27f9465b944689
  );
  const content = props.posts.map((post) =>
    19bcd6b2eb431bc35ca7af1f5e43e263
      684271ed9684bde649abda8831d4d355{post.title}39528cedfa926ea0c01e69ef5b2ea9b0
      e388a4556c0f65e1904146cc1a846bee{post.content}94b3e26ee717c64999d7867364b1b4a3
    16b28748ea4df4d9c2150843fecfba68
  );
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      {sidebar}
      231a563c997aa9e3e0ae614bd16728b0
      {content}
    16b28748ea4df4d9c2150843fecfba68
  );
}

10. Forms and Controlled Components

Handling Form Data

Handling form data in React involves managing the state of the form fields.

import React, { useState } from 'react';

const MyForm = () => {
  const [value, setValue] = useState('');

  const handleChange = (event) => {
    setValue(event.target.value);
  };

  const handleSubmit = (event) => {
    event.preventDefault();
    alert('A name was submitted: ' + value);
  };

  return (
    a9bf9d9bedc9abd7dd4d836a79412b6a
      2e1cf0710519d5598b1f0f14c36ba674
        Name:
        504d17b0f6b03dc75f5b399918bed261
      8c1ecd4bb896b2264e0711597d40766c
      92e8cbd9feac6a729893ae422743759e
    f5a47148e367a6035fd7a2faa965022e
  );
};

export default MyForm;

Controlled vs Uncontrolled Components

Controlled components are those that are controlled by React state. Uncontrolled components are those that maintain their own internal state.

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: '' };

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({ value: event.target.value });
  }

  handleSubmit(event) {
    alert('A name was submitted: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      244054e4e8cabd44c7e8193aa6f63fb5
        2e1cf0710519d5598b1f0f14c36ba674
          Name:
          733698873fa50da8fa779e67406daca2
        8c1ecd4bb896b2264e0711597d40766c
        92e8cbd9feac6a729893ae422743759e
      f5a47148e367a6035fd7a2faa965022e
    );
  }
}

Using Refs for Uncontrolled Components

Refs provide a way to access DOM nodes or React elements created in the render method.

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.input = React.createRef();
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleSubmit(event) {
    alert('A name was submitted: ' + this.input.current.value);
    event.preventDefault();
  }

  render() {
    return (
      244054e4e8cabd44c7e8193aa6f63fb5
        2e1cf0710519d5598b1f0f14c36ba674
          Name:
          63001db5982f3e60a1b9208a578f6cf9
        8c1ecd4bb896b2264e0711597d40766c
        92e8cbd9feac6a729893ae422743759e
      f5a47148e367a6035fd7a2faa965022e
    );
  }
}

Form Validation

Form validation ensures that user inputs are valid.

const MyForm = () => {
  const [name, setName] = useState('');
  const [email, setEmail] = useState('');
  const [error, setError] = useState('');

  const handleSubmit = (event) => {
    event.preventDefault();
    if (!name || !email) {
      setError('Name and Email are required');
    } else {
      setError('');
      // Submit form
    }
  };

  return (
    a9bf9d9bedc9abd7dd4d836a79412b6a
      {error && e388a4556c0f65e1904146cc1a846bee{error}94b3e26ee717c64999d7867364b1b4a3}
      2e1cf0710519d5598b1f0f14c36ba674
        Name:
        e6680c943276b2479743ae48aa2c3c4d setName(e.target.value)} />
      8c1ecd4bb896b2264e0711597d40766c
      2e1cf0710519d5598b1f0f14c36ba674
        Email:
        7448c870435c8466d6415b4cd5e57af3 setEmail(e.target.value)} />
      8c1ecd4bb896b2264e0711597d40766c
      92e8cbd9feac6a729893ae422743759e
    f5a47148e367a6035fd7a2faa965022e
  );
};

export default MyForm;

11. React Router

React Router is a library for routing in React applications. It allows you to handle navigation and rendering of different components based on the URL.

Setting Up React Router

1. Install React Router:
   

   npm install react-router-dom
   

2. Set Up Routes:
   

   import React from 'react';
   import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
   
   const Home = () => <h2>Home</h2>;
   const About = () => <h2>About</h2>;
   
   const App = () => {
     return (
       <Router>
         <Switch>
           <Route exact path="/" component={Home} />
           <Route path="/about" component={About} />
         </Switch>
       </Router>
     );
   };
   
   export default App;
   

Route Parameters

You can use route parameters to capture values from the URL.

import React from 'react';
import { BrowserRouter as Router, Route,

 Switch, useParams } from 'react-router-dom';

const User = () => {
  const { id } = useParams();
  return c1a436a314ed609750bd7c7d319db4daUser ID: {id}2e9b454fa8428549ca2e64dfac4625cd;
};

const App = () => {
  return (
    a7f2cf15f06fbef780c6b2609731da81
      da7c15ee158c884a4ad5d56e941eda87
        ce6eeaea0ee015d7c7834a2da08622ed
      3fd1eab6a3ee1fe92fde6d97b1988f07
    80ecef3d33cd6309af735c93542122ea
  );
};

export default App;

Nested Routes

Nested routes allow you to render sub-components within a parent component.

import React from 'react';
import { BrowserRouter as Router, Route, Switch, Link, useRouteMatch } from 'react-router-dom';

const Topic = ({ match }) => 684271ed9684bde649abda8831d4d355Requested Topic ID: {match.params.topicId}39528cedfa926ea0c01e69ef5b2ea9b0;

const Topics = ({ match }) => {
  let { path, url } = useRouteMatch();
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      c1a436a314ed609750bd7c7d319db4daTopics2e9b454fa8428549ca2e64dfac4625cd
      ff6d136ddc5fdfeffaf53ff6ee95f185
        25edfb22a4f469ecb59f1190150159c6
          b725e8e2701aa5ef3b10cf4a4a8d3034Components06f735b502bd5273dad825215f7c405b
        bed06894275b65c1ab86501b08a632eb
        25edfb22a4f469ecb59f1190150159c6
          8e1f596f8f79d213858f4f3ff1b58fceProps v. State06f735b502bd5273dad825215f7c405b
        bed06894275b65c1ab86501b08a632eb
      929d1f5ca49e04fdcb27f9465b944689
      da7c15ee158c884a4ad5d56e941eda87
        61f0fa4321c44137e30312030a9c0e20
          684271ed9684bde649abda8831d4d355Please select a topic.39528cedfa926ea0c01e69ef5b2ea9b0
        c14cb6b64e224f4e5a949337b2570e26
        9d194525d14decb3df37718d52f26590
      3fd1eab6a3ee1fe92fde6d97b1988f07
    16b28748ea4df4d9c2150843fecfba68
  );
};

const App = () => {
  return (
    a7f2cf15f06fbef780c6b2609731da81
      dc6dce4a544fdca2df29d5ac0ea9906b
        ff6d136ddc5fdfeffaf53ff6ee95f185
          25edfb22a4f469ecb59f1190150159c6
            4edbf5b784c612aafd5036a3e2d83c2dHome06f735b502bd5273dad825215f7c405b
          bed06894275b65c1ab86501b08a632eb
          25edfb22a4f469ecb59f1190150159c6
            b640d72ae84e3bad89e0179d1e328243Topics06f735b502bd5273dad825215f7c405b
          bed06894275b65c1ab86501b08a632eb
        929d1f5ca49e04fdcb27f9465b944689
        231a563c997aa9e3e0ae614bd16728b0
        da7c15ee158c884a4ad5d56e941eda87
          bbb3e500d9f4f89883020186a2ddbb4a
          f0e68096eeb3ed9fbd81056f58b8d5f3
        3fd1eab6a3ee1fe92fde6d97b1988f07
      16b28748ea4df4d9c2150843fecfba68
    80ecef3d33cd6309af735c93542122ea
  );
};

export default App;

Redirects and Navigation

You can use the Redirect component to redirect to a different route programmatically.

import React from 'react';
import { BrowserRouter as Router, Route, Switch, Redirect } from 'react-router-dom';

const Home = () => c1a436a314ed609750bd7c7d319db4daHome2e9b454fa8428549ca2e64dfac4625cd;
const About = () => c1a436a314ed609750bd7c7d319db4daAbout2e9b454fa8428549ca2e64dfac4625cd;

const App = () => {
  return (
    a7f2cf15f06fbef780c6b2609731da81
      da7c15ee158c884a4ad5d56e941eda87
        bbb3e500d9f4f89883020186a2ddbb4a
        c9dc43901ba2d8c28c3c578e571107b7
        7709cf1d190ed88bc67892b77f43d992
      3fd1eab6a3ee1fe92fde6d97b1988f07
    80ecef3d33cd6309af735c93542122ea
  );
};

export default App;

12. Context API

The Context API provides a way to pass data through the component tree without having to pass props down manually at every level.

Creating Context

To create a context, use React.createContext.

const MyContext = React.createContext();

Consuming Context

To consume a context value, use the useContext hook in functional components or Context.Consumer in class components.

const MyComponent = () => {
  const value = useContext(MyContext);
  return dc6dce4a544fdca2df29d5ac0ea9906b{value}16b28748ea4df4d9c2150843fecfba68;
};

Context with Functional Components

const MyComponent = () => {
  return (
    b689c0d1a993785138e54bc7cc21f63f
      ea5c314853a1992950c8ee28be9bd72f
    8e66e6aff1f0a13ebced51b2c1b5d182
  );
};

const AnotherComponent = () => {
  const value = useContext(MyContext);
  return dc6dce4a544fdca2df29d5ac0ea9906b{value}16b28748ea4df4d9c2150843fecfba68;
};

Updating Context

To update context, create a provider component with state.

const MyProvider = ({ children }) => {
  const [value, setValue] = useState('Hello');
  return (
    682880ab8c111fd3ec21b55025046065
      {children}
    8e66e6aff1f0a13ebced51b2c1b5d182
  );
};

const MyComponent = () => {
  const { value, setValue } = useContext(MyContext);
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      {value}
      5ddc0978355752d4bf828563dc007a14 setValue('Updated Value')}>Update65281c5ac262bf6d81768915a4a77ac0
    16b28748ea4df4d9c2150843fecfba68
  );
};

Context Best Practices

• Avoid overusing context: Use context sparingly and only for global data.

• Use multiple contexts: Separate concerns by using multiple contexts.

• Memoize context values: Use useMemo to avoid unnecessary re-renders.

13. Hooks

Hooks are functions that let you use state and other React features in functional components.

Basic Hooks (useState, useEffect)

• useState: Adds state to functional components.

• useEffect: Performs side effects in functional components.

Additional Hooks (useContext, useReducer)

• useContext: Accesses context values.

• useReducer: Manages complex state logic.
  

const initialState = { count: 0 };

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    default:
      throw new Error();
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, initialState);
  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      Count: {state.count}
      5ddc0978355752d4bf828563dc007a14 dispatch({ type: 'increment' })}>+65281c5ac262bf6d81768915a4a77ac0
      5ddc0978355752d4bf828563dc007a14 dispatch({ type: 'decrement' })}>-65281c5ac262bf6d81768915a4a77ac0
    16b28748ea4df4d9c2150843fecfba68
  );
}

Custom Hooks

Custom hooks are functions that encapsulate logic and can be reused across components.

const useFetch = (url) => {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetch(url)
      .then((response) => response.json())
      .then((data) => setData(data));
  }, [url]);

  return data;
};

const MyComponent = () => {
  const data = useFetch('https://api.example.com/data');
  return dc6dce4a544fdca2df29d5ac0ea9906b{data ? JSON.stringify(data) : 'Loading...'}16b28748ea4df4d9c2150843fecfba68;
};

Rules of Hooks

• Call hooks at the top level: Do not call hooks inside loops, conditions, or nested functions.

• Only call hooks from React functions: Call hooks from functional components or custom hooks.

14. Higher-Order Components (HOC)

Higher-Order Components (HOC) are functions that take a component and return a new component.

Understanding HOCs

HOCs are used to add additional functionality to components.

const withLogging = (WrappedComponent) => {
  return (props) => {
    console.log('Rendering', WrappedComponent.name);
    return 31403eb0b6940459d9df68e14fc75564;
  };
};

Creating HOCs

const EnhancedComponent = withLogging(MyComponent);

Using HOCs

const MyComponent = (props) => {
  return dc6dce4a544fdca2df29d5ac0ea9906bMy Component16b28748ea4df4d9c2150843fecfba68;
};

const EnhancedComponent = withLogging(MyComponent);

HOC Best Practices

• Do not mutate the original component: Return a new component.

• Use display names for debugging: Set displayName on the HOC for better debugging.

15. Error Boundaries

Error boundaries are React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI.

Implementing Error Boundaries

Error boundaries catch errors during rendering, in lifecycle methods, and in constructors of the whole tree below them.

class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError(error) {
    return { hasError: true };
  }

  componentDidCatch(error, errorInfo) {
    // You can also log the error to an error reporting service
    console.log(error, errorInfo);
  }

  render() {
    if (this.state.hasError) {
      return 4a249f0d628e2318394fd9b75b4636b1Something went wrong.473f0a7621bec819994bb5020d29372a;
    }

    return this.props.children; 
  }
}

Catching Errors

Error boundaries catch errors in the render method and in lifecycle methods.

const MyComponent = () => {
  throw new Error('An error occurred');
  return dc6dce4a544fdca2df29d5ac0ea9906bMy Component16b28748ea4df4d9c2150843fecfba68;
};

const App = () => {
  return (
    e61056d4a8a9030688e67f3b8b93a2b5
      c91df85aa2a01a1e069f702d655e9491
    cb28499deb11178577145cfc441388a7
  );
};

Error Boundaries Best Practices

• Use error boundaries to catch errors in components: Use error boundaries to catch and display errors in UI components.

• Log errors for debugging: Log errors to external services for debugging.

16. React Performance Optimization

Memoization

Memoization helps to avoid re-rendering components unnecessarily.

import React, { memo } from 'react';

const MyComponent = memo(({ value }) => {
  return dc6dce4a544fdca2df29d5ac0ea9906b{value}16b28748ea4df4d9c2150843fecfba68;
});

Code Splitting

Code splitting helps to load only the necessary code and improve performance.

import React, { Suspense, lazy } from 'react';

const OtherComponent = lazy(() => import('./OtherComponent'));

const MyComponent = () => {
  return (
    <Suspense fallback={dc6dce4a544fdca2df29d5ac0ea9906bLoading...16b28748ea4df4d9c2150843fecfba68}>
      8f13323f6387d4fb51abaf18b61b3667
    08ee156419279e45977839a62de7dfe8
  );
};

Lazy Loading

Lazy loading helps to load components only when they are needed.

import React, { Suspense, lazy } from 'react';

const Other

Component = lazy(() => import('./OtherComponent'));

const MyComponent = () => {
  return (
    <Suspense fallback={dc6dce4a544fdca2df29d5ac0ea9906bLoading...16b28748ea4df4d9c2150843fecfba68}>
      8f13323f6387d4fb51abaf18b61b3667
    08ee156419279e45977839a62de7dfe8
  );
};

useMemo and useCallback

• useMemo: Memoizes expensive calculations.

• useCallback: Memoizes functions.
  

const MyComponent = ({ value }) => {
  const memoizedValue = useMemo(() => {
    return computeExpensiveValue(value);
  }, [value]);

  const memoizedCallback = useCallback(() => {
    doSomething(value);
  }, [value]);

  return (
    dc6dce4a544fdca2df29d5ac0ea9906b
      {memoizedValue}
      f1e0750461fc4f521cd24a5533f81591Click me65281c5ac262bf6d81768915a4a77ac0
    16b28748ea4df4d9c2150843fecfba68
  );
};

React Developer Tools

Use React Developer Tools to identify performance bottlenecks.

17. Testing in React

Jest and React Testing Library

Jest and React Testing Library are popular tools for testing React components.

Writing Tests

• Snapshot Testing: Capture the rendered component and compare it with a saved snapshot.

• Unit Testing: Test individual components and functions.

• Integration Testing: Test the integration between components and services.
  

import { render, screen } from '@testing-library/react';
import MyComponent from './MyComponent';

test('renders MyComponent', () => {
  render(c91df85aa2a01a1e069f702d655e9491);
  const element = screen.getByText(/My Component/i);
  expect(element).toBeInTheDocument();
});

18. React Best Practices

Component Structure

• Organize components by feature: Group related components together.

• Use descriptive names: Use clear and descriptive names for components and props.

• Keep components small: Break down large components into smaller, reusable components.

State Management

• Lift state up: Lift state to the nearest common ancestor.

• 使用 Context 进行全局状态：使用 Context API 进行全局状态管理。

造型

• 使用 CSS 模块：使用 CSS 模块来实现作用域和模块化样式。

• 使用样式组件：使用样式组件进行动态样式设置。

表现

• 避免不必要的重新渲染：使用记忆化和 React 内置的性能优化工具。

• 使用代码拆分：拆分代码以仅加载必要的组件。

测试

• 编写全面的测试：为应用程序的所有关键部分编写测试。

• 使用快照测试：使用快照测试来捕获意外的更改。

结论

React.js 是一个用于构建现代 Web 应用程序的强大库。通过理解和利用其核心概念，您可以构建高效、可维护和可扩展的应用程序。这份备忘单是帮助您掌握 React.js 的综合指南，涵盖从基本概念到高级主题的所有内容。

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