nl_tokens: Handles the provided { @code upgradeneeded } event that occurred during opening a database that was not blocked . The function handles database schema upgrade .
pl_tokens: function upgradeDatabaseSchema ( databaseName , <mask> , migrationPromise , database , transaction , sortedSchemaDescriptors , migrationPromiseResolver , migrationPromiseRejector ) { executeMigrationListeners ( databaseName , event . oldVersion , event . newVersion , migrationPromise ) let migrator = new DatabaseMigrator ( database , transaction , sortedSchemaDescriptors , event . oldVersion ) return PromiseSync . resolve ( ) . then ( ( ) => { return migrator . executeMigration ( ) } ) . then ( ( ) => { migrationPromiseResolver ( ) } ) . catch ( ( error ) => { migrationPromiseRejector ( error ) throw error } ) }