doSomeDatabaseWork().then(result => {
    // Success
}).catch('UnknownError', e => {
    // Failed with UnknownError
    console.error ("Unknown error: " + e.message);
}).catch(Error, e => {
    // Any other error derived from standard Error
    console.error ("Error: " + e.message);
}).catch(e => {
    // Other error such as a string was thrown
    console.error (e);
});

db.on('error', function (error) {
    switch (error.name) {
        // errnames.Unknown ==="UnknownError"
        case Dexie.errnames.Unknown:
            console.error ("Unknown error");
            break;
        default:
            console.error ("error: " + e);
    }
});