Auto saving to localStorage with MobX

autoStore.js

import mobx from "mobx"
import store from "store"

export default function(_this) {
  let firstRun = true

  // will run on change
  mobx.autorun(() => {
    // on load check if there's an existing store on localStorage and extend the store
    if (firstRun) {
      const existingStore = store.get("store")
      
      if (existingStore) {
        mobx.extendObservable(_this, existingStore)
      }
    }

    // from then on serialize and save to localStorage
    store.set("store", mobx.toJS(_this))
  })

  firstRun = false
}

todoStore.js

import mobx, { computed, observable } from "mobx"
import autoSave from "./autoSave"

const initialTodoStore = {
  todos: ["buy milk", "buy eggs"]
}

class TodoStore {
  constructor() {
    // set initial mock up examples
    this.todos = initialTodoStore  // or []
    
    // in the future it will over run it and save to store
    autoSave(this)
  }

  @observable todos
  @observable filter = ""

  @computed get filteredTodos() {
    const filter = new RegExp(this.filter, "i")

    return this.todos.filter(todo => !this.filter || filter.test(todo))
  }
}

const todoStore = window.todoStore = new TodoStore

export default todoStore

In case anyone is interested what I did to solve my problem was to use the 'mobx-persist-store' library to write my store data to the localStorage.
Then (inside my store) I added a store event listener and update it every time I detect a change.

in mobxStore.ts

import { makePersistable, hydrateStore } from 'mobx-persist-store';

class Store {
  // --- STORE STATE VARS ---
  dashboard = {
    isVisible: true,
  };

  constructor() {
    makePersistable(this, { name: 'mobxStore',
      properties: ['dashboard'],
      storage: window.localStorage }).finally(() => {});
   }

  // --- SHOW/HIDE DASHBOARD ---
  setDashboard(visible: boolean) {
    this.dashboard.isVisible = visible;
  }
}

const myStore = new Store();

window.addEventListener('storage', (e) => {
  if (e.key === 'mobxStore') {
    myStore.hydrateStore().catch(() => {});
  }
});

export default myStore;

in a different window (but same domain http://localhost:3000/test )the component:

import React from 'react';

import { observer } from 'mobx-react';
import store from 'store/mobxStore';

const FakeComponent = () => {
  const visible = store.dashboard.isVisible;
  return (
    <div>
      {store.dashboard.isVisible ? <span>Dashboard visible</span> : <span>Dashboard Invisible</span>}
      <br />
      <div onClick={() => store.setDashboard(!visible)} >"Switch dashboard visibility"</div>
    </div>
  );
};

export default observer(FakeComponent);