Migrate from previous version of a database

The third (optional) parameter of the openDB() function is an object that can contain an upgrade function called only if the version number is higher than the current installed database version. In that function body you can upgrade the structure (stores and indexes) of the db:

const name = 'mydbname'
const version = 1
openDB(name, version, {
  upgrade(db, oldVersion, newVersion, transaction) {
    console.log(oldVersion)
  }
})

In this callback, you can check from which version the user is updating, and perform some operations accordingly.

You can perform a migration from a previous database version using this syntax

(async () => {
  //...
  const dbName = 'mydbname'
  const storeName = 'store0'
  const version = 1

  const db = await openDB(dbName, version, {
    upgrade(db, oldVersion, newVersion, transaction) {
      switch (oldVersion) {
        case 0: // no db created before
          // a store introduced in version 1
          db.createObjectStore('store1')
        case 1:
          // a new store in version 2
          db.createObjectStore('store2', { keyPath: 'name' })
      }
      db.createObjectStore(storeName)
    }
  })
})()

Lessons in this unit: