React 自动优化：再见 memo、useMemo 和 useCallback？-js教程-PHP中文网

React Automatic Optimization: Goodbye memo, useMemo, and useCallback?

React 19 为性能优化带来了显着改进，特别是在处理记忆化方面。让我们探讨一下 memo、useMemo 和 useCallback 是如何演变的以及它们现在默认情况下是如何优化的。

React 中记忆化的演变

之前在 React 18 中，开发人员必须仔细考虑何时使用记忆技术来防止不必要的重新渲染并优化性能。 React 19 通过引入自动优化来改变这种范式，使这些工具更加高效，并且在许多情况下是不必要的。

React 19 中的备忘录：更智能的组件记忆

React 19 的备忘录现在对于何时重新渲染组件变得更加智能。框架自动跟踪 prop 更改及其对组件输出的影响。

示例1：基本道具比较

// React 18
const UserCard = memo(({ user, onUpdate }) => {
  return (
    <div>
      <h2>{user.name}</h2>
      <button onClick={onUpdate}>Update</button>
    </div>
  );
});

// React 19
// memo is now automatically optimized
const UserCard = ({ user, onUpdate }) => {
  return (
    <div>
      <h2>{user.name}</h2>
      <button onClick={onUpdate}>Update</button>
    </div>
  );
});

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示例 2：嵌套组件

// React 18
const CommentThread = memo(({ comments, onReply }) => {
  return (
    <div>
      {comments.map(comment => (
        <Comment 
          key={comment.id}
          {...comment}
          onReply={onReply}
        />
      ))}
    </div>
  );
});

// React 19
const CommentThread = ({ comments, onReply }) => {
  return (
    <div>
      {comments.map(comment => (
        <Comment 
          key={comment.id}
          {...comment}
          onReply={onReply}
        />
      ))}
    </div>
  );
});

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useMemo：自动值记忆

React 19 的 useMemo 现已优化，可以自动检测记忆化何时有益，从而减少手动优化的需要。

示例 1：昂贵的计算

// React 18
const ExpensiveChart = ({ data }) => {
  const processedData = useMemo(() => {
    return data.map(item => ({
      ...item,
      value: complexCalculation(item.value)
    }));
  }, [data]);

  return <ChartComponent data={processedData} />;
};

// React 19
const ExpensiveChart = ({ data }) => {
  // React 19 automatically detects expensive operations
  const processedData = data.map(item => ({
    ...item,
    value: complexCalculation(item.value)
  }));

  return <ChartComponent data={processedData} />;
};

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示例 2：对象引用

// React 18
const UserProfile = ({ user }) => {
  const userStyles = useMemo(() => ({
    background: user.premium ? 'gold' : 'silver',
    border: `2px solid ${user.active ? 'green' : 'gray'}`
  }), [user.premium, user.active]);

  return <div>



<h3>
  
  
  Example 3: Derived State
</h3>



<pre class="brush:php;toolbar:false">// React 18
const FilteredList = ({ items, filter }) => {
  const filteredItems = useMemo(() => 
    items.filter(item => item.category === filter),
    [items, filter]
  );

  return <List items={filteredItems} />;
};

// React 19
const FilteredList = ({ items, filter }) => {
  // React 19 automatically optimizes derived state
  const filteredItems = items.filter(item => item.category === filter);
  return <List items={filteredItems} />;
};

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useCallback：更智能的函数记忆

React 19 的 useCallback 现在在函数稳定性和引用相等性方面更加智能。

示例 1：事件处理程序

// React 18
const TodoList = ({ todos, onToggle }) => {
  const handleToggle = useCallback((id) => {
    onToggle(id);
  }, [onToggle]);

  return todos.map(todo => (
    <TodoItem 
      key={todo.id}
      {...todo}
      onToggle={handleToggle}
    />
  ));
};

// React 19
const TodoList = ({ todos, onToggle }) => {
  // React 19 automatically maintains function stability
  const handleToggle = (id) => {
    onToggle(id);
  };

  return todos.map(todo => (
    <TodoItem 
      key={todo.id}
      {...todo}
      onToggle={handleToggle}
    />
  ));
};

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示例 2：具有依赖关系的回调

// React 18
const SearchComponent = ({ onSearch, searchParams }) => {
  const debouncedSearch = useCallback(
    debounce((term) => {
      onSearch({ ...searchParams, term });
    }, 300),
    [searchParams, onSearch]
  );

  return <input onChange={e => debouncedSearch(e.target.value)} />;
};

// React 19
const SearchComponent = ({ onSearch, searchParams }) => {
  // React 19 handles function stability automatically
  const debouncedSearch = debounce((term) => {
    onSearch({ ...searchParams, term });
  }, 300);

  return <input onChange={e => debouncedSearch(e.target.value)} />;
};

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示例 3：复杂事件处理

// React 18
const DataGrid = ({ data, onSort, onFilter }) => {
  const handleHeaderClick = useCallback((column) => {
    onSort(column);
    onFilter(column);
  }, [onSort, onFilter]);

  return (
    <table>
      <thead>
        {columns.map(column => (
          <th key={column} onClick={() => handleHeaderClick(column)}>
            {column}
          </th>
        ))}
      </thead>
      {/* ... */}
    </table>
  );
};

// React 19
const DataGrid = ({ data, onSort, onFilter }) => {
  // React 19 optimizes function creation and stability
  const handleHeaderClick = (column) => {
    onSort(column);
    onFilter(column);
  };

  return (
    <table>
      <thead>
        {columns.map(column => (
          <th key={column} onClick={() => handleHeaderClick(column)}>
            {column}
          </th>
        ))}
      </thead>
      {/* ... */}
    </table>
  );
};

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