为什么React Hooks改变了一切：全球开发者的视角

            class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      

        
Count: {this.state.count}
        Increment
      
    );
  }
}

            

              
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import React, { useState } from 'react';

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

  const increment = () => {
    setCount(count + 1);
  };

  return (
    

      
Count: {count}
      Increment
    
  );
}

            

              
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class UserProfile extends React.Component {
  state = {
    user: null,
    loading: true,
  };

  async componentDidMount() {
    const response = await fetch('/api/user');
    const data = await response.json();
    this.setState({ user: data, loading: false });
  }

  render() {
    if (this.state.loading) {
      return 
Loading...
;
    }
    return 
Welcome, {this.state.user.name}
;
  }
}

            

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

function UserProfile({ userId }) {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    async function fetchUser() {
      const response = await fetch(`/api/user/${userId}`);
      const data = await response.json();
      setUser(data);
      setLoading(false);
    }
    fetchUser();
  }, [userId]); // Dependency array ensures effect re-runs if userId changes

  if (loading) {
    return 
Loading...
;
  }

  return 
Welcome, {user.name}
;
}

            

              
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import { useState, useEffect } from 'react';

function useFetch(url) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch(url);
        if (!response.ok) {
          throw new Error(`HTTP error! status: ${response.status}`);
        }
        const result = await response.json();
        setData(result);
        setError(null);
      } catch (err) {
        setError(err);
        setData(null);
      } finally {
        setLoading(false);
      }
    };

    fetchData();
  }, [url]); // Re-fetch if URL changes

  return { data, loading, error };
}

export default useFetch;

            

              
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import React from 'react';
import useFetch from './useFetch'; // Assuming useFetch is in a separate file

function UserList() {
  const { data: users, loading, error } = useFetch('/api/users');

  if (loading) return 
Loading users...
;
  if (error) return 
Error loading users: {error.message}
;

  return (
    

      {users.map(user => (
        
{user.name}
      ))}
    
  );
}

function ProductDetails({ productId }) {
  const { data: product, loading, error } = useFetch(`/api/products/${productId}`);

  if (loading) return 
Loading product...
;
  if (error) return 
Error loading product: {error.message}
;

  return (
    

      
{product.name}
      
{product.description}
    
  );
}

            

              
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// In Context.js
// const MyContext = React.createContext();

// In ConsumerComponent.js
// import MyContext from './Context';
// function ConsumerComponent() {
//   return (
//     
//       {value => (
//         
Value from context: {value}
//       )}
//     
//   );
// }

            

              
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import React, { useContext } from 'react';
// import MyContext from './Context'; // Assuming MyContext is exported

function ConsumerComponent() {
  const value = useContext(MyContext);
  return 
Value from context: {value}
;
}

            

              
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