svelte-playground/src/lib/stores/todos.js

import { onMount } from 'svelte';
import { writable } from 'svelte/store';

const localStore = (key, initial) => {
	const toString = (value) => JSON.stringify(value, null, 2);
	const toObject = JSON.parse;

	if (process.browser) {
		if (localStorage.getItem(key) === null) {
			localStorage.setItem(key, toString(initial));
		}

		const saved = toObject(localStorage.getItem(key));

		const { subscribe, set, update } = writable(saved);

		return {
			subscribe,
			set: (value) => {
				// both return and save in the local storage
				localStorage.setItem(key, toString(value));
				return set(value);
			},
			update
		};
	}
};

// export const todos = localStore('todo-store', []);
console.log('here we are: ' + typeof window);
export const todos = writable([]);