reducer.js

const initialState = {
  addedIds: [],
  quantityById: {},
  kitById: {},

  itemFormula: {
    byId: {
      1: {
        id: 1,
        itemId: 1,
        formulas: [1, 2]
      },
      2: {
        id: 2,
        itemId: 1,
        formulas: []
      }
    },
    allIds: [1, 2]
  },
  quantityByItemFormulaId: {}
}

const itemFormula = (state = initialState.itemFormula, action) => {
  switch (action.type) {
    case CART_ADD_ITEM:

      const idx = state.allIds.find(id => {
        let pivot = state.byId[id]

        return pivot.itemId === action.itemsId &&
          isEqual(pivot.formulas, action.formulas.sort())
      })

      if (typeof idx !== 'undefined') {
        return state
      }

      const newId = state.allIds.slice(-1)[0] + 1
      const byId = {...state.byId, [newId]: {}}
      const allIds = [...state.allIds, newId]

      return { ...state, byId: byId, allIds: allIds }
    case CART_DELETE_ITEM:
      return state.filter(itemId => action.itemId !== itemId )
    default:
      return state
  }
}