NgRx selector with customized equal function

selector with deep equal

import { isEqual } from 'lodash';
import {
  createFeatureSelector,
  createSelector,
  createSelectorFactory,
  defaultMemoize,
} from '@ngrx/store';
import * as fromFlightBooking from './flight-booking.reducer';

export const selectFlightBookingState = createFeatureSelector<
  fromFlightBooking.State
>(fromFlightBooking.flightBookingFeatureKey);

export const selectFlights = createSelector(
  selectFlightBookingState,
  (state) => state.flights
);

export const selectFirstFlight = createSelector(selectFlights, (flights) => {
  console.log('selectFirstFlight');
  if (flights.length) {
    return flights[0];
  } else {
    return null;
  }
});

// https://github.com/ngrx/platform/issues/1157
const customMemoizer = (aFn) => defaultMemoize(aFn, isEqual);
const createDeepEqualSelector = createSelectorFactory(customMemoizer);

export const flightName = createSelector(selectFirstFlight, (flight) => {
  console.log('selectFlightName');
  return flight ? { name: flight.from } : '';
});

export const heavyCalculation = createDeepEqualSelector(flightName, () => {
  console.log('doing heavy calculation');
  return true;
});