Create and manage localStorage collection asynchronously.

asynLocalCollection.js

const asyncLocalStorage = {
  createCollection: (collectionName, data) => Promise.resolve().then(() => {
    if (!(data instanceof Object)) {
      throw Error('Local storage collection can be only valid JSON.');
    }
    return localStorage.setItem(collectionName, JSON.stringify(data));
  }),
  getCollection: collectionName => Promise.resolve().then(() =>
    localStorage.getItem(collectionName)),
  setItem: (key, value, collectionName) => Promise.resolve()
    .then(() => localStorage.getItem(collectionName))
    .then(collectionData => JSON.parse(collectionData))
    .then((parsed) => { const newData = Object(parsed); newData[key] = value; return newData; })
    .then(newData => localStorage.setItem(collectionName, JSON.stringify(newData))),
  getItem: (key, collectionName) => Promise.resolve()
    .then(() => localStorage.getItem(collectionName))
    .then(collectionData => JSON.parse(collectionData)[key]),
  removeItem: (key, value, collectionName) => Promise.resolve()
    .then(() => localStorage.getItem(collectionName))
    .then(collectionData => JSON.parse(collectionData))
    .then((parsed) => { const newData = Object(parsed); delete newData[key]; return newData; })
    .then(newData => localStorage.setItem(collectionName, JSON.stringify(newData))),
};