详解Jotai Immer如何实现undo redo功能示例详解
作者：wesin
背景
之前项目中一直使用redux作为全局状态库使用，然后最近有个大功能改造，涉及undo、redo等功能影响，小伙伴推荐jotai来替代redux。于是稍事研究了下，对比redux，果然简单了很多，去除了redux里厚重的模板代码，使用也很方便。 所以为啥一开始不直接就jotai呢，还抱着redux啃了半天？反思了下，可能原因是redux名声更响，当年撸flutter、撸ios的时候就被这个名词轰炸了，所以一想到全局状态库，就直接选了它，忽略了前端发展的日新月异，早就有了更好的替代品，经验主义作祟，引以为戒。另一个原因估计是论坛里光顾着摸鱼沸点了，忽略了介绍jotai的文章。 小伙伴又推荐了结合immer的功能来实现undo、redo功能。好嘛，翻了翻文档，immer不就是个简化immutable对象修改的工具吗？咋就跟undo、redo搭上关系了。经解释，方知原来immer高级篇有produceWithPatches的功能支持对象的undo以及redo功能。 当然undo、redo功能我找了找其实是有现有库的，只是代码翻了翻多年没更新了，下载过来连示例都运行不起来，算了，配合以上的jotai、immer功能，貌似直接简单撸一个也不难的样子，那么就开干吧。
代码不多，直接上了
import { Patch, applyPatches, produceWithPatches } from "immer";
import { atomWithImmer } from "jotai-immer";
import { atom, createStore } from "jotai/vanilla";
import { JSONSchema7 } from "json-schema";
interface HistoryInfo {
patch: Patch;
inverse: Patch;
}
interface HistoryState {
undo: HistoryInfo[];
redo: HistoryInfo[];
}
// 业务代码涉及的undo、redo数据
export interface HistoryItem {
businessA: { [key: string]: any };
businessB: Record<string, JSONSchema7>;
businessC: any;
}
// 构建一个undo、redo的数据起点
const historyItemAtom = atomWithImmer<HistoryItem>({
businessA: {},
businessB: {},
businessC: {},
});
// 触发需要保存的undo的一个操作事件
export const fireHistoryAtom = atom(0.0);
export const businessAAtom = atomWithImmer<{ [key: string]: any }>({});
export const businessBAtom = atomWithImmer<Record<string, JSONSchema7>>({});
export const businessCAtom = atomWithImmer<any>();
export const historyAtom = atomWithImmer<HistoryState>({
undo: [],
redo: [],
});
export const store = createStore();
// 页面数据加载完毕写入初始化history
export const dataInit = () => {
const newHis: HistoryItem = {
businessA: store.get(businessAAtom),
businessB: store.get(businessBAtom),
businessC: store.get(businessCAtom),
};
store.set(historyItemAtom, newHis);
};
// ----------------------------------------------------------------
// atom subscriptions
store.sub(fireHistoryAtom, () => {
const newHis: HistoryItem = {
businessA: store.get(businessAAtom),
businessB: store.get(businessBAtom),
businessC: store.get(businessCAtom),
};
const oldHis = store.get(historyItemAtom);
const [next, patch, inverse] = produceWithPatches(oldHis, (draft) => {
draft = newHis;
return draft;
});
store.set(historyItemAtom, next);
store.set(historyAtom, (draft) => {
draft.undo.push({
patch: patch[0],
inverse: inverse[0],
});
draft.redo = [];
});
});
export const fireHistory = () => {
setTimeout(() => {
store.set(fireHistoryAtom, Math.random());
}, 20);
};
// 执行业务代码
const doAction = (item: HistoryItem) => {
store.set(businessAAtom, (draft) => {
draft = item.businessA;
return draft;
});
store.set(businessBAtom, (draft) => {
draft = item.businessB;
return draft;
});
store.set(businessCAtom, (draft) => {
draft = item.businessC;
return draft;
});
store.set(historyItemAtom, (draft) => {
draft = item;
return draft;
});
};
export const undoAction = () => {
const history = store.get(historyAtom);
if (history.undo.length === 0) {
return;
}
const old = history.undo[history.undo.length - 1];
const currentItem = store.get(historyItemAtom);
const item = applyPatches(currentItem, [old.inverse]);
doAction(item);
store.set(historyAtom, (draft) => {
const current = draft.undo.pop();
if (current) {
draft.redo.push(current);
}
});
};
export const redoAction = () => {
const history = store.get(historyAtom);
if (history.redo.length === 0) {
return;
}
const old = history.redo[history.redo.length - 1];
const currentItem = store.get(historyItemAtom);
const item = applyPatches(currentItem, [old.patch]);
doAction(item);
store.set(historyAtom, (draft) => {
const current = draft.redo.pop();
if (current) {
draft.undo.push(current);
}
});
};大致讲下思路
定义 HistoryItem 作为undo、redo所需要恢复的业务数据，可随意扩展。undo、redo本质上就是你点了undo按钮后你的数据需要恢复到上一个状态。当业务复杂了之后，你一次操作可能包含了多个数据的变化，而你undo的操作应该是把这些数据一起还原。所以把涉及到变化的数据都包装在一起，形成一个historyitem。通过 immer提供的produceWithPatches生成撤销和恢复数据， 存在 HistoryState 的undo 里，然后你点击undo按钮，把数据从undo中取出，放入redo中。然后把数据状态通过jotai全局修改，差不多就完成了。
简单的jotai使用是不需要store参与的，这里为了取数据、改数据方便，所以使用了store的监听和set功能。 使用store的代码也很简单，直接在最外层包个provider即可
<Provider store={mainStore}>
<MainPage />
</Provider>使用方式应该挺简单的吧。 当你做完需要undo的操作后，调用fireHistory()函数即可。页面的undo、redo按钮可以直接把事件映射到undoAction、redoAction。至于undo、redo按钮是否能点的功能可以直接读取 historyAtom 里面undo、redo的数组长度。
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