How to save Mobx state in sessionStorage

Question

Trying to essentially accomplish this https://github.com/elgerlambert/redux-localstorage which is for Redux but do it for Mobx. And preferably would like to use sessionStorage.

Answer 1

Posting the example from here: https://mobx.js.org/best/store.html

This shows a cleaner method of detecting value changes, though not necessarily local storage.

import {observable, autorun} from 'mobx';
import uuid from 'node-uuid';

export class TodoStore {
    authorStore;
    transportLayer;
    @observable todos = [];
    @observable isLoading = true;

    constructor(transportLayer, authorStore) {
        this.authorStore = authorStore; // Store that can resolve authors for us
        this.transportLayer = transportLayer; // Thing that can make server requests for us
        this.transportLayer.onReceiveTodoUpdate(updatedTodo => this.updateTodoFromServer(updatedTodo));
        this.loadTodos();
    }

    /**
     * Fetches all todo's from the server
     */
    loadTodos() {
        this.isLoading = true;
        this.transportLayer.fetchTodos().then(fetchedTodos => {
            fetchedTodos.forEach(json => this.updateTodoFromServer(json));
            this.isLoading = false;
        });
    }

    /**
     * Update a todo with information from the server. Guarantees a todo
     * only exists once. Might either construct a new todo, update an existing one,
     * or remove an todo if it has been deleted on the server.
     */
    updateTodoFromServer(json) {
        var todo = this.todos.find(todo => todo.id === json.id);
        if (!todo) {
            todo = new Todo(this, json.id);
            this.todos.push(todo);
        }
        if (json.isDeleted) {
            this.removeTodo(todo);
        } else {
            todo.updateFromJson(json);
        }
    }

    /**
     * Creates a fresh todo on the client and server
     */
    createTodo() {
        var todo = new Todo(this);
        this.todos.push(todo);
        return todo;
    }

    /**
     * A todo was somehow deleted, clean it from the client memory
     */
    removeTodo(todo) {
        this.todos.splice(this.todos.indexOf(todo), 1);
        todo.dispose();
    }
}

export class Todo {

    /**
     * unique id of this todo, immutable.
     */
    id = null;

    @observable completed = false;
    @observable task = "";

    /**
     * reference to an Author object (from the authorStore)
     */
    @observable author = null;

    store = null;

    /**
     * Indicates whether changes in this object
     * should be submitted to the server
     */
    autoSave = true;

    /**
     * Disposer for the side effect that automatically
     * stores this Todo, see @dispose.
     */
    saveHandler = null;

    constructor(store, id=uuid.v4()) {
        this.store = store;
        this.id = id;

        this.saveHandler = reaction(
            // observe everything that is used in the JSON:
            () => this.asJson,
            // if autoSave is on, send json to server
            (json) => {
                if (this.autoSave) {
                    this.store.transportLayer.saveTodo(json);
                }
            }
        );
    }

    /**
     * Remove this todo from the client and server
     */
    delete() {
        this.store.transportLayer.deleteTodo(this.id);
        this.store.removeTodo(this);
    }

    @computed get asJson() {
        return {
            id: this.id,
            completed: this.completed,
            task: this.task,
            authorId: this.author ? this.author.id : null
        };
    }

    /**
     * Update this todo with information from the server
     */
    updateFromJson(json) {
        // make sure our changes aren't send back to the server
        this.autoSave = false;
        this.completed = json.completed;
        this.task = json.task;
        this.author = this.store.authorStore.resolveAuthor(json.authorId);
        this.autoSave = true;
    }

    dispose() {
        // clean up the observer
        this.saveHandler();
    }
}