React & Immer

egghead.io 第八课: 使用 Immer 和 useState，或者 useImmer。

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useState + Immer

useState hook 假定存储在其中的任何 state 都被视为不可变的。使用 Immer 可以大大简化 React 组件状态的深度更新。下面的例子展示了如何使用 produce 和 useState ，可以在 CodeSandbox 试试。

import React, { useCallback, useState } from "react";
import {produce} from "immer";

const TodoList = () => {
  const [todos, setTodos] = useState([
    {
      id: "React",
      title: "Learn React",
      done: true
    },
    {
      id: "Immer",
      title: "Try Immer",
      done: false
    }
  ]);

  const handleToggle = useCallback((id) => {
    setTodos(
      produce((draft) => {
        const todo = draft.find((todo) => todo.id === id);
        todo.done = !todo.done;
      })
    );
  }, []);

  const handleAdd = useCallback(() => {
    setTodos(
      produce((draft) => {
        draft.push({
          id: "todo_" + Math.random(),
          title: "A new todo",
          done: false
        });
      })
    );
  }, []);

  return (<div>{*/ See CodeSandbox */}</div>)
}

useImmer

由于所有 state 的更新都使用 produce 包装的更新模式，所以我们可以通过将更新模式包装在 use-immer 包中来简化上述操作

import React, { useCallback } from "react";
import { useImmer } from "use-immer";

const TodoList = () => {
  const [todos, setTodos] = useImmer([
    {
      id: "React",
      title: "Learn React",
      done: true
    },
    {
      id: "Immer",
      title: "Try Immer",
      done: false
    }
  ]);

  const handleToggle = useCallback((id) => {
    setTodos((draft) => {
      const todo = draft.find((todo) => todo.id === id);
      todo.done = !todo.done;
    });
  }, []);

  const handleAdd = useCallback(() => {
    setTodos((draft) => {
      draft.push({
        id: "todo_" + Math.random(),
        title: "A new todo",
        done: false
      });
    });
  }, []);

  // etc

完整的 demo 请参阅 CodeSandbox

useReducer + Immer

与 useState 类似，useReducer 也与 Immer 巧妙结合，如 CodeSandbox 所示：

import React, {useCallback, useReducer} from "react"
import {produce} from "immer"

const TodoList = () => {
    const [todos, dispatch] = useReducer(
        produce((draft, action) => {
            switch (action.type) {
                case "toggle":
                    const todo = draft.find(todo => todo.id === action.id)
                    todo.done = !todo.done
                    break
                case "add":
                    draft.push({
                        id: action.id,
                        title: "A new todo",
                        done: false
                    })
                    break
                default:
                    break
            }
        }),
        [
            /* initial todos */
        ]
    )

    const handleToggle = useCallback(id => {
        dispatch({
            type: "toggle",
            id
        })
    }, [])

    const handleAdd = useCallback(() => {
        dispatch({
            type: "add",
            id: "todo_" + Math.random()
        })
    }, [])

    // etc
}

useImmerReducer

同上，可以通过 use-immer 包中的 useImmerReducer 简化 (demo)

import React, { useCallback } from "react";
import { useImmerReducer } from "use-immer";

const TodoList = () => {
  const [todos, dispatch] = useImmerReducer(
    (draft, action) => {
      switch (action.type) {
        case "toggle":
          const todo = draft.find((todo) => todo.id === action.id);
          todo.done = !todo.done;
          break;
        case "add":
          draft.push({
            id: action.id,
            title: "A new todo",
            done: false
          });
          break;
        default:
          break;
      }
    },
    [ /* initial todos */ ]
  );

  //etc

Redux + Immer

Redux + Immer 在 Redux Toolkit 的文档中被广泛介绍。对于没有 Redux Toolkit 的 Redux，可以应用与上面应用于 useReducer 相同的技巧：使用 produce 包装 reducer 函数，您可以安全地修改 draft！

例子:

import {produce} from "immer"

// 初始 state
const INITIAL_STATE = [
    /* 一系列 todos */
]

const todosReducer = produce((draft, action) => {
    switch (action.type) {
        case "toggle":
            const todo = draft.find(todo => todo.id === action.id)
            todo.done = !todo.done
            break
        case "add":
            draft.push({
                id: action.id,
                title: "A new todo",
                done: false
            })
            break
        default:
            break
    }
})