ngrx-normalizing-state-before.ts

// State
export interface State {
  customers: Customer[];
  selectedCustomer: Customer;
}

// Reducer
export function reducer(state, action) {
  switch (action.type) {
    ...
    case EDIT_CUSTOMER:
      return {
        customers: state.customers.map(c => (c.id === action.payload.id ? action.payload : c)),
        selectedCustomer:
          state.selectedCustomer && state.selectedCustomer.id === action.payload.id
            ? action.payload
            : state.selectedCustomer,
      };
    ...
  }
}

// Selectors
export const selectCustomers = createSelector(selectCustomersState, state => state.customers);
export const selectSelectedCustomer = createSelector(selectCustomersState, state => state.selectedCustomer);