async localstorage

asyncLocalStorage.js

// Source: https://stackoverflow.com/questions/42921220/is-any-solution-to-do-localstorage-setitem-in-asynchronous-way-in-javascript

// localStorage is a synchronous API. You could defer the setItem method execution with the Promise object, giving them an asynchronous behaviour:

const asyncLocalStorage = {
    setItem: function (key, value) {
        return Promise.resolve().then(function () {
            localStorage.setItem(key, value);
        });
    },
    getItem: function (key) {
        return Promise.resolve().then(function () {
            return localStorage.getItem(key);
        });
    }
};

// Demo
const data = Date.now() % 1000;
asyncLocalStorage.setItem('mykey', data).then(function () {
    return asyncLocalStorage.getItem('mykey');
}).then(function (value) {
    console.log('Value has been set to:', value);
});
console.log('waiting for value to become ' + data + 
            '. Current value: ', localStorage.getItem('mykey'));
// See it run on repl.it, as SO snippets do not allow the use of localStorage.

// With the newer async/await syntax, this asyncLocalStorage can be written as:

const asyncLocalStorage = {
    setItem: async function (key, value) {
        await null;
        return localStorage.setItem(key, value);
    },
    getItem: async function (key) {
        await null;
        return localStorage.getItem(key);
    }
};