Let db be connection’s .

Let transaction be a new upgrade transaction with connection used as . The scope of transaction includes every in connection.

Set database’s upgrade transaction to transaction.

Unset transaction’s .

Let old version be db’s version.

Set the version of db to version. This change is considered part of the , and so if the transaction is aborted, this change is reverted.

to run these steps:

1. Set request’s result to connection.

3. Set transaction’s .

4. Let didThrow be the result of running the steps to fire a version change event named at request with old version and version.

5. Unset transaction’s .

Wait for transaction to finish.