useeffect使用指南
    英文回答：
    useEffect is a hook in React that allows us to perform side effects in functional components. It is similar to componentDidMount, componentDidUpdate, and componentWillUnmount lifecycle methods in class components.
    To use useEffect, we need to import it from the 'react' package. We can then call it inside our functional component, passing in a callback function as the first argument. This callback function will be executed after the component has rendered.
    Here is an example of how to use useEffect:
    javascript.
    import React, { useEffect } from 'react';
    function MyComponent() {。
      useEffect(() => {。
        console.log('Component rendered');
      });
      return (。
        <div>。
          <h1>Hello, World!</h1>。
        </div>。
      );
    }。
    In this example, the callback function passed to useEffect simply logs a message to the console. This function will be called after the component has rendered for the first time, as
well as after every subsequent render.
    We can also provide a second argument to useEffect, which is an array of dependencies. This allows us to specify when the effect should be re-run. If any of the dependencies change, the effect will be re-run.
    Here is an example that demonstrates the use of dependencies:
    javascript.
    import React, { useEffect, useState } from 'react';
    function MyComponent() {。
      const [count, setCount] = useState(0);
      useEffect(() => {。
react to的用法        console.log('Count changed:', count);
      }, [count]);
      return (。
        <div>。
          <h1>Count: {count}</h1>。
          <button onClick={() => setCount(count + 1)}>Increment</button>。
        </div>。
      );
    }。
    In this example, the effect will only be re-run if the value of `count` changes. This is useful when we want to perform certain actions only when specific data changes.

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