This code saves a loads data from the localStorage object on the browser.

DataController.js

'use strict';

class DataController {
}

DataController.load = loadLocalStorage
DataController.save = saveLocalStorage

function loadLocalStorage() {
  let rawData = localStorage.getItem('masters3d');
  if (rawData !== null) {
    let data = JSON.parse(rawData)
    return {success:true, data}
  } else {
    return {success:false, data:{}}
  }
}

/** @param {Object} data */
function saveLocalStorage(data) {
  localStorage.setItem('masters3d', JSON.stringify(data))
}