Used in https://medium.com/@timdeschryver/ngrx-immer-7fe4a0d43508

catalog.immer-reducer.ts

export const reducer = produce<State, CatalogActions>((draft, action) => {
  switch (action.type) {
    case CatalogActionTypes.Load:
      action.payload.products.forEach(product => {
        draft.products[product.sku] = product;
        draft.productSkus.push(product.sku);
      });
  }
}, initialState);