Persist values between web pages in localstorage

store.js

/* 
Persist values between web pages in localstorage
 Handles data objects to any depth
usage:
  let store = new Store;
  let value = store.db.path.to.field.value;
  store.update = {section: {field: value}};
*/
class Store {
  constructor() { this.init(); }

  // Reset localStorage if asked in the querystring
  init() {
    let params = new URLSearchParams(window.location.search);
    if (params.get('reset')) { this.clear(); }
  }

  // Get localStorage.values
  //  let obj = store.db;
  get db() {
    return JSON.parse(localStorage.values
      ? localStorage.values
      : this.clear());
   }

  // Update localStorage.values
  //   store.update = {section: {field: value}};
  set update(obj) {
    let values = this.db;
    values = this.merge(values, obj);
    localStorage.values = JSON.stringify(values);
  }

  // Deep merge `source` data object to a `target` recursively
  // https://gist.github.com/ahtcx/0cd94e62691f539160b32ecda18af3d6
  merge(target, source) {
    for (const key of Object.keys(source)) {
      if (source[key] instanceof Object) {
        Object.assign(source[key], this.merge(target[key], source[key]));
      }
    }
    Object.assign(target || {}, source)
    return target
  }

  // Reset localStorage to default values
  clear() {
    localStorage.clear();
    let database = {};
    localStorage.values = JSON.stringify(database);
    return localStorage.values;
  }

  // Browser friendly JSON display of localStorage values
  settings() {
    return '<pre>\n' + JSON.stringify(this.db, null, 2) + '\n</pre>';
  }

  // Save localStorage to a local file
  exportData() {
    return btoa(JSON.stringify({ values: this.db }, null, 2));
  }

  // Read localStorage from exported file
  importData(data) {
    this.update = JSON.parse(data).values;
  }
}