Keeps a failed request from aborting the upgrade: an error event left uncancelled aborts its
transaction — here the version-change one, so the whole open would fail.
Parameters
request: IDBRequest
The request whose failure must stay its own.
step: string
The migration step, as the log names it — e.g. "v7 repair".
what: string
What the request was doing, completing "could not …".
Returns void
Example
spare(store.put(record), "v7 repair", "write the record");
Keeps a failed request from aborting the upgrade: an error event left uncancelled aborts its transaction — here the version-change one, so the whole open would fail.