indexedDB.example.js

let openRequest = indexedDB.open("test", 5);
let messages = [
  { id: 0, message: 'pepepe' },
  { id: 1, message: 'paco' },
]

openRequest.onsuccess = function(ev) {
  console.log('SUCCESS')
  console.log(ev)

  let db = ev.target.result
  add(db, messages[0])
  add(db, messages[1])

  setTimeout(() => {
    read(db)
  }, 200)
}

openRequest.onupgradeneeded = function(ev) {
  console.log('UPGRADED NEEDED')
  console.log(ev)

  let db = ev.target.result

  // If objectStore exists, we'll recreate it
  if (db.objectStoreNames.contains('messages')) {
    db.deleteObjectStore('messages')
  }

  db.createObjectStore('messages', { keyPath: 'id' })
}

function add(db, obj) {
  let messageStore = db.transaction("messages", "readwrite").objectStore('messages')
  messageStore.add(obj)
}

function read(db) {
  let store = db.transaction("messages").objectStore('messages')
  let request = store.getAll()

  request.onsuccess = function(e) {
      console.log(e.target.result)
  }
}