redux vs redux-toolkit 及源码实现

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本文作者：霜序

前言

为何讲这个内容？以为后续大家会使用 redux-toolkit，资产上周做了 redux-toolkit 的升级顺便了解了相关内容，产出了这篇文章。

另外补齐一下在 React 数据流这个知识板块的完整性。

• React 中的数据流管理
• 认识一下 Mobx

在之前的周分享中已经分享过了React 中的数据流，react-redux 的一些实现，redux 中中间件的实现，以及 Mobx 的使用以及丐版实现。

对于 Redux 本身尚未涉及，趁着使用 redux-toolkit 的机会一起了解一下 Redux 的实现。

Redux-Toolkit

Redux-Toolkit 是 基于 Redux 的二次封装，开箱即用的 Redux 工具，比 Redux 更加简单方便。

Why to use Redux-Toolkit?

• "Configuring a Redux store is too complicated"
• "I have to add a lot of packages to get Redux to do anything useful"
• "Redux requires too much boilerplate code"

Toolkit 使用

Redux 该有的概念，Toolkit 其实都拥有的，只是他们使用的方式不同，例如 reducer / actions 等等，在 Toolkit 中都是随处可见的。

configureStore

创建 store，代码内部还是调用的 Redux 的 createStore 方法

const store = configureStore({
    reducer: {
        counter: counterReducer,
        user: userReducer,
    },
});

createAction + createReducer

• createAction
  
  创建 Redux 中的 action 创建函数

function createAction(type, prepareAction?)

redux 中 action 的创建以及使用

const updateName = (name: string) => ({ type: "user/UPDATE_NAME", name });
const updateAge = (age: number) => ({ type: "user/UPDATE_AGE", age });

Toolkit 中 action 的创建以及使用

// 第一种
const updateName = createAction<{ name: string }>("user/UPDATE_NAME");
const updateAge = createAction<{ age: number }>("user/UPDATE_AGE");

updateName();  // { type: 'user/UPDATE_NAME', payload: undefined }
updateName({ name: "FBB" }); // { type: 'user/UPDATE_NAME', payload: { name: 'FBB' } }
updateAge({ age: 18 });

// 第二种
const updateName = createAction("user/UPDATE_NAME", (name: string) => ({
  payload: {
    name,
  },
}));
const updateAge = createAction("user/UPDATE_AGE", (age: number) => ({
  payload: {
    age,
  },
}));

updateName("FBB");
updateAge(18);

• createReducer
  
  创建 Redux reducer 的函数

:::info

createReducer 使用 Immer 库，可以在 reducer 中直接对状态进行修改，而不需要手动编写不可变性的逻辑  

:::

Redux 中 reducer 的创建

export const userReducer = (
  state = initialUserState,
  action: { type: string; [propName: string]: any }
) => {
  switch (action.type) {
    case "user/UPDATE_NAME":
      return { ...state, name: action.name };
    case "user/UPDATE_AGE":
      return { ...state, age: action.age };
    default:
      return state;
  }
};

Toolkit 中 reducer 的创建

export const userReducer = createReducer(initialUserState, (builder) => {
  builder
    .addCase(updateAge, (state, action) => {
      state.age = action.payload.age;
    })
    .addCase(updateName, (state, action) => {
      state.name = action.payload.name;
    });
});

toolkit 提供的 createAction 和 createReducer 能够帮我们简化 Redux 中一些模版语法，但是整体的使用还是差不多的，我们依旧需要 action 文件和 reducer 文件，做了改善但是不多。

redux demo   toolkit createReducer demo

createSlice

接受初始状态、reducer 函数对象和 slice name 的函数，并自动生成与 reducer 和 state 对应的动作创建者和动作类型

const userSlice = createSlice({
  name: "user",
  initialState: {
    age: 22,
    name: "shuangxu",
  },
  reducers: {
    updateName: (state, action: PayloadAction<string>) => {
      state.name = action.payload;
    },
    updateAge: (state, action: PayloadAction<number>) => {
      state.age = action.payload;
    },
  },
})

使用 createSlice 创建一个分片，每一个分片代表某一个业务的数据状态处理。在其中可以完成 action 和 reducer 的创建。

export const userSliceName = userSlice.name;
export const { updateAge, updateName } = userSlice.actions;
export const userReducer = userSlice.reducer;

const store = configureStore({
  reducer: {
    [counterSliceName]: counterReducer,
    [userSliceName]: userReducer,
  },
});

toolkit slice demo

在 Toolkit 中直接使用 createSlice 更加方便，能够直接导出 reducer 和 action，直接在一个方法中能够获取到对应内容不在需要多处定义。

Redux 源码实现

简单的状态管理

所谓的状态其实就是数据，例如用户中的 name

let state = {
  name: "shuangxu"
}

// 使用状态
console.log(state.name)

// 更改状态
state.name = "FBB"

上述代码中存在问题，当我们修改了状态之后无法通知到使用状态的函数，需要引入发布订阅模式来解决这个问题

const state = {
  name: "shuangxu",
};
const listeners = [];

const subscribe = (listener) => {
  listeners.push(listener);
};

const changeName = (name) => {
  state.name = name;
  listeners.forEach((listener) => {
    listener?.();
  });
};

subscribe(() => console.log(state.name));

changeName("FBB");
changeName("LuckyFBB");

在上述代码中，我们已经实现了更改变量能够通知到对应的监听函数。但是上述代码并不通用，需要将公共方法封装起来。

const createStore = (initialState) => {
  let state = initialState;
  let listeners = [];

  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
      listeners = listeners.filter((fn) => fn !== listener);
    };
  };

  const changeState = (newState) => {
    state = { ...state, ...newState };
    listeners.forEach((listener) => {
      listener?.();
    });
  };

  const getState = () => state;

  return {
    subscribe,
    changeState,
    getState,
  };
};

// example
const { getState, changeState, subscribe } = createStore({
  name: "shuangxu",
  age: 19,
});

subscribe(() => console.log(getState().name, getState().age));

changeState({ name: "FBB" });   // FBB 19
changeState({ age: 26 });       // FBB 26

changeState({ sex: "female" });

约束状态管理器

上述的实现能够更改状态和监听状态的改变。但是上述改变 state 的方式过于随便了，我们可以任意修改 state 中的数据，changeState({ sex: "female" })，即使 sex 不存在于 initialState 中，所以我们需要约束只能够修改 name/age 属性

通过一个 plan 函数来规定UPDATE_NAME和UPDATE_AGE方式更新对应属性

const plan = (state, action) => {
  switch (action.type) {
    case "UPDATE_NAME":
      return {
        ...state,
        name: action.name,
      };
    case "UPDATE_AGE":
      return {
        ...state,
        age: action.age,
      };
    default:
      return state;
  }
};

更改一下 createStore 函数

const createStore = (plan, initialState) => {
  let state = initialState;
  let listeners = [];

  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
      listeners = listeners.filter((fn) => fn !== listener);
    };
  };

  const changeState = (action) => {
    state = plan(state, action);
    listeners.forEach((listener) => {
      listener?.();
    });
  };

  const getState = () => state;

  return {
    subscribe,
    changeState,
    getState,
  };
};

const { getState, changeState, subscribe } = createStore(plan, {
  name: "shuangxu",
  age: 19,
});

subscribe(() => console.log(getState().name, getState().age));

changeState({ type: "UPDATE_NAME", name: "FBB" });
changeState({ type: "UPDATE_AGE", age: "28" });
changeState({ type: "UPDATE_SEX", sex: "female" });

代码中的 plan 就是 redux 中的 reducer，changeState 就是 dispatch。

拆分 reducer

reducer 做的事情比较简单，接收 oldState，通过 action 更新 state。

但是实际项目中可能存在不同模块的 state，如果都把 state 的执行计划写在同一个 reducer 中庞大有复杂。

因此在常见的项目中会按模块拆分不同的 reducer，最后在一个函数中将 reducer 合并起来。

const initialState = {
  user: { name: "shuangxu", age: 19 },
  counter: { count: 1 },
};

// 对于上述 state 我们将其拆分为两个 reducer
const userReducer = (state, action) => {
  switch (action.type) {
    case "UPDATE_NAME":
      return {
        ...state,
        name: action.name,
      };
    case "UPDATE_AGE":
      return {
        ...state,
        age: action.age,
      };
    default:
      return state;
  }
};

const counterReducer = (state, action) => {
  switch (action.type) {
    case "INCREMENT":
      return {
        count: state.count + 1,
      };
    case "DECREMENT":
      return {
        ...state,
        count: state.count - 1,
      };
    default:
      return state;
  }
};

// 整合 reducer
const combineReducers = (reducers) => {
  // 返回新的 reducer 函数
  return (state = {}, action) => {
    const newState = {};
    for (const key in reducers) {
      const reducer = reducers[key];
      const preStateForKey = state[key];
      const nextStateForKey = reducer(preStateForKey, action);
      newState[key] = nextStateForKey;
    }
    return newState;
  };
};

代码跑起来！！

const reducers = combineReducers({
  counter: counterReducer,
  user: userReducer,
});

const store = createStore(reducers, initialState);
store.subscribe(() => {
  const state = store.getState();
  console.log(state.counter.count, state.user.name, state.user.age);
});
store.dispatch({ type: "UPDATE_NAME", name: "FBB" });  // 1 FBB 19
store.dispatch({ type: "UPDATE_AGE", age: "28" });     // 1 FBB 28
store.dispatch({ type: "INCREMENT" });                 // 2 FBB 28
store.dispatch({ type: "DECREMENT" });                 // 1 FBB 28

拆分 state

在上一节的代码中，我们 state 还是定义在一起的，会造成 state 树很庞大，在项目中使用的时候我们都在 reducer 中定义好 initialState 的。

在使用 createStore 的时候，我们可以不传入 initialState，直接使用store = createStore(reducers)。因此我们要对这种情况作处理。

拆分 state 和 reducer 写在一起。

const initialUserState = { name: "shuangxu", age: 19 };

const userReducer = (state = initialUserState, action) => {
  switch (action.type) {
    case "UPDATE_NAME":
      return {
        ...state,
        name: action.name,
      };
    case "UPDATE_AGE":
      return {
        ...state,
        age: action.age,
      };
    default:
      return state;
  }
};

const initialCounterState = { count: 1 };

const counterReducer = (state = initialCounterState, action) => {
  switch (action.type) {
    case "INCREMENT":
      return {
        count: state.count + 1,
      };
    case "DECREMENT":
      return {
        ...state,
        count: state.count - 1,
      };
    default:
      return state;
  }
};

更改 createStore 函数，可以自动获取到每一个 reducer 的 initialState

const createStore = (reducer, initialState = {}) => {
  let state = initialState;
  let listeners = [];

  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
      listeners = listeners.filter((fn) => fn !== listener);
    };
  };

  const dispatch = (action) => {
    state = reducer(state, action);
    listeners.forEach((listener) => {
      listener?.();
    });
  };

  const getState = () => state;

  // 仅仅用于获取初始值
  dispatch({ type: Symbol() });

  return {
    subscribe,
    dispatch,
    getState,
  };
};

dispatch({ type: Symbol() })代码能够实现如下效果：

• createStore 的时候，一个不匹配任何 type 的 action，来触发state = reducer(state, action)
• 每个 reducer 都会进到 default 项，返回 initialState

Redux-Toolkit 源码实现

configureStore

接受一个含有 reducer 的对象作为参数，内部调用 redux 的 createStore 创建出 store

import { combineReducers, createStore } from "redux";

export function configureStore({ reducer }: any) {
  const rootReducer = combineReducers(reducer);
  const store = createStore(rootReducer);
  return store;
}

createAction

const updateName = createAction<string>("user/UPDATE_NAME");
const updateName = createAction("user/UPDATE_NAME", (name: string) => ({
  payload: {
    name,
  },
}));

updateName("FBB");

通过上面的示例，能够分析出来 createAction 返回的是一个函数，接受第一个参数 type 返回{ type: 'user/UPDATE_NAME', payload: undefined }；对于具体的 payload 值需要传入第二个参数来改变

export const createAction = (type: string, preAction?: Function) => {
  function actionCreator(...args: any[]) {
    if (!preAction)
      return {
        type,
        payload: args[0],
      };
    const prepared = preAction(...args);
    if (!prepared) {
      throw new Error("prepareAction did not return an object");
    }
    return {
      type,
      payload: prepared.payload,
    };
  }
  actionCreator.type = type;
  return actionCreator;
};

createReducer

export const userReducer = createReducer(initialUserState, (builder) => {
  builder
    .addCase(updateAge, (state, action) => {
      state.age = action.payload.age;
    })
    .addCase(updateName, (state, action) => {
      state.name = action.payload.name;
    });
});

每一个 reducer 都是一个函数(state = initialState, action) => {}，因此 createReducer 返回值为函数

通过一个 createReducer 函数，内部还需要知道每一个 action 对应的操作

import { produce as createNextState } from "immer";

export const createReducer = (
  initialState: any,
  builderCallback: (builder: any) => void
) => {
  const actionsMap = executeReducerBuilderCallback(builderCallback);
  return function reducer(state = initialState, action: any) {
    const caseReducer = actionsMap[action.type];
    if (!caseReducer) return state;
    return createNextState(state, (draft: any) =>
      caseReducer(draft, action)
                          );
  };
};

// 通过 createReducer 的第二个参数，构建出 action 对应的操作方法
export const executeReducerBuilderCallback = (
  builderCallback: (builder: any) => void
) => {
  const actionsMap: any = {};
  const builder = {
    addCase(typeOrActionCreator: any, reducer: any) {
      const type =
        typeof typeOrActionCreator === "string"
        ? typeOrActionCreator
        : typeOrActionCreator.type;
      actionsMap[type] = reducer;
      return builder;
    },
  };
  builderCallback(builder);
  return actionsMap;
};

createSlice

const counterSlice = createSlice({
  name: "counter",
  initialState: {
    count: 1,
  },
  reducers: {
    increment: (state: any) => {
      state.count += 1;
    },
    decrement: (state: any) => {
      state.count -= 1;
    },
  },
});

const counterSliceName = counterSlice.name;
const { increment, decrement } = counterSlice.actions;
const counterReducer = counterSlice.reducer;

createSlice 返回的是一个对象{ name, actions, reducer }，接受{ name, initialState, reducers }三个参数。通过 reducers 中相关参数得到对应的 actions 和 reducer。

在 createSlice 中主要还是靠 createAction 和 createReducer 方法。通过 name 和 reducers 的每一个属性拼接成为 action.type，调用 createReducer 遍历 reducers 的属性添加 case

import { createAction } from "./createAction";
import { createReducer } from "./createReducer";

export default function createSlice({ name, initialState, reducers }: any) {
  const reducerNames = Object.keys(reducers);

  const actionCreators: any = {};
  const sliceCaseReducersByType: any = {};

  reducerNames.forEach((reducerName) => {
    const type = `${name}/${reducerName}`;
    const reducerWithPrepare = reducers[reducerName];
    actionCreators[reducerName] = createAction(type);
    sliceCaseReducersByType[type] = reducerWithPrepare;
  });

  function buildReducer() {
    return createReducer(initialState, (builder) => {
      for (let key in sliceCaseReducersByType) {
        builder.addCase(key, sliceCaseReducersByType[key]);
      }
    });
  }

  return {
    name,
    actions: actionCreators,
    reducer: (state: any, action: any) => {
      const _reducer = buildReducer();
      return _reducer(state, action);
    },
  };
}

总结

在本文讲解了 Redux-Toolkit 基础使用，从 redux 的源码出发解析了 redux-toolkit 的源码，从源码中也能够看出来 toolkit 的实现是基于 redux 来实现的，且使用上也大同小异，无破坏性变更。

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