⚕️ 🥑 ⛵️ 改善useReducer 🥊 🚭 🕞

随着应用状态的出现useReducer和useContext管理，它变得更加便捷，并且不再需要使用Redux。

当我第一次放弃Redux而不是标准版本时，useReducer我感到缺少一些有用的功能：

useSelector。可以优化所使用的组件的渲染useContext与memo。
唯一的调度。简化更新应用程序状态的过程，因为您无需为每个应用程序使用单独的调度useReducer。
缓存。您不必担心缓存所有人useReducer。

然后，我决定尝试useReducer通过添加这三个功能来提高标准。这个想法已经发展成为一个新的小型库，我称之为Flex Reducer。

趣味事实！

Flex Reducer在其useReducer任何useContext实现中均未使用。

让我们以典型的Todo App为例，了解使用标准useReducer+useContext和Flex Reducer的利弊。

首先，让我们创建一个主文件，在其中渲染React树。

// index.js
import TodoApp from "./TodoApp";

const rootElement = document.getElementById("root");
ReactDOM.render(
  <TodoApp />,
  rootElement
);

注意：不再合并减速器，创建商店和提供者。万岁！:)

现在，让我们使用编写主要的Todo App组件useReducer。

// TodoApp.js
import { useReducer, createContext, useMemo } from 'react';
import AddTodo from './AddTodo';
import TodoList from './TodoList';

export const AppContext = createContext(null);
const cache = {};

export default function TodoApp() {
  const [state, dispatch] = useReducer(reducer, cache.state || initialState);
  cache.state = state;
  const actions = useMemo(() => ({
    setInput: (value) => {
      dispatch({
        type: 'SET_INPUT', 
        payload: value
      })
    },
    addTodo: ({ id, content }) => {
      dispatch({
        type: 'ADD_TODO',
        payload: { id, content }
      })
    }
  }), []);
  return (
    <AppContext.Provider value=[state, actions]>
      <div className="todo-app">
        <h1>{state.title}</h1>
        <input value={state.input} onChange={e => actions.setInput(e.target.value)} />
        <AddTodo />
        <TodoList />
      </div>
    </AppContext>
  );
}

看起来不错。现在同样的事情，只是使用Flex Reducer。

// TodoApp.js
import { useFlexReducer, dispatch } from 'flex-reducer';
import AddTodo from './AddTodo';
import TodoList from './TodoList';

export const setInput = (value) => dispatch({
  type: SET_INPUT,
  payload: value
});
export const addTodo = ({ id, content }) => dispatch({
  type: ADD_TODO,
  payload: { id, content }
});

export default function TodoApp() {
  const [state] = useFlexReducer('app', reducer, initialState);
  return (
    <div className="todo-app">
      <h1>{state.title}</h1>
      <input value={state.input} onChange={e => setInput(e.target.value)} />
      <AddTodo />
      <TodoList />
    </div>
  );
}

, .

:

React Context.
.
actions dispatch.

re-renders Add Todo button.

.

// AddTodo.js
import { useContext, memo } from 'react';
import { appContext } from './TodoApp';

const genId = () => Math.rand();

const AddTodo = memo(({ input, actions }) => {
  function handleAddTodo() {
    if (content) {
      actions.addTodo({ id: genId(), content: input });
      actions.setInput('');
    }
  }
  return (
    <button onClick={handleAddTodo}>
      Add Todo
    </button>
  );
})

export default const MemoizedAddTodo = () => {
  const [state, actions] = useContext(appContext);
  return (
    <AddTodo input={state.input} actions={actions} />
  );
}

useContext AddTodo render memo. -, useContext props.

Flex Reducer.

// AddTodo.js
import { useSelector } from 'flex-reducer';
import { addTodo, setInput } from "./TodoApp";

const genId = () => Math.rand();

export default const AddTodo = React.memo(() => {
  const content = useSelector(state => state.app.input);
  function handleAddTodo() {
    if (content) {
      addTodo({ id: genId(), content });
      setInput('');
    }
  }
  return (
    <button onClick={handleAddTodo}>
      Add Todo
    </button>
  );
})

. -. useSelector, re-render input.

, , Flex Reducer .

remote data, , react-query.

useReducer.

// TodoApp.js
import { useReducer, createContext, useMemo } from 'react';
import { useQuery } from 'react-query';
import AddTodo from './AddTodo';
import TodoList from './TodoList';

export const AppContext = createContext(null);
const cache = {};

export default function TodoApp() {
  const [reducerState, dispatch] = useReducer(reducer, cache.state || initialState);
  cache.state = reducerState;
  const actions = useMemo(() => ({
    setInput: (value) => {
      dispatch({
        type: 'SET_INPUT', 
        payload: value
      })
    },
    addTodo: ({ id, content }) => {
      dispatch({
        type: 'ADD_TODO',
        payload: { id, content }
      })
    }
  }), []);

  const todos = useQuery('todos', fetchTodoList);
  const state = { ...reducerState, todos };

  return (
    <AppContext.Provider value=[state, actions]>
      <div className="todo-app">
        <h1>{state.title}</h1>
        <input value={state.input} onChange={e => actions.setInput(e.target.value)} />
        <AddTodo />
        <TodoList />
      </div>
    </AppContext>
  );
}

. .

Flex Reducer.

// TodoApp.js
import { useFlexReducer, dispatch } from 'flex-reducer';
import { useQuery } from 'react-query';
import AddTodo from './AddTodo';
import TodoList from './TodoList';

export const setInput = (value) => dispatch({
  type: SET_INPUT,
  payload: value
});
export const addTodo = ({ id, content }) => dispatch({
  type: ADD_TODO,
  payload: { id, content }
});
export const setTodos = (todos) => dispatch({
  type: SET_TODOS,
  payload: todos
});

export default function TodoApp() {
  const [state] = useFlexReducer('app', reducer, initialState);
  const todos = useQuery('todos', fetchTodoList);
  React.useEffect(() => {
    setTodos(todos);
  }, [todos]);

  return (
    <div className="todo-app">
      <h1>{state.title}</h1>
      <input value={state.input} onChange={e => setInput(e.target.value)} />
      <AddTodo />
      <TodoList />
    </div>
  );
}

todos query.

使用useReducer+useContext管理应用程序状态非常方便。但这需要对上下文和缓存进行仔细的“手动”工作。

Flex Reducer会注意这一点，提高代码的可读性，使编写优化更容易，memo并减少了工作量。但是，当以声明方式使用远程数据时（如使用react-query），就会出现问题。

注意！

Flex Reducer只是一个实验，尚未在生产中使用。

谢谢阅读。任何想法表示赞赏。

您可以在此处找到Todo应用程序的工作示例。

链接到Flex Reducer存储库

改善useReducer

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