Immutability-helper allows declarative updates that do not update the original state. It should be used in all reducers because it:
helps prevent accidental update of the previous state
is usually more concise than manually making deep clones of state (easier to read and maintain).
Editor reducers already use it. Other reducers in zanata-frontend should all use it. Audit the reducers and update so that all are using immutability-helper. Reducers should have tests before this update.