This might be pure if you can guarantee no one is changing txns - for example - while updatePersonBalance runs. Throw in a async fn in there and all bets are of

This might be pure if you can guarantee no one is changing txns - for example - while updatePersonBalance runs. Throw in a async fn in there and all bets are off. Looking at state mgmt solutions for JS today, many will require or recommend immutable data - for very good reasons.