StyleGuide - When to use pure and Impure pipes

[johnpapa]

To be discussed ...

I copied several of these from early discussions and will list them as issues for future discussion after ngConf

cc // @mgechev @wardbell

• Use impure pipes only when they need to hold state.

  Why?: The change detection can optimize pure pipes since they hold the referential transparency property.

• Wherever stateful (impure) pipes are required, implement the OnDestroy interface.

  Why? It is likely that a stateful pipe may contain state that should be cleaned up when a binding is destroyed. For example, a subscription to a stream of data may need to be disposed, or an interval may need to be cleared.

[johnpapa]

@joeeames may have some thoughts on this