Mobx VS Reselect comparison

mobx.js

const store = makeAutoObservable({
  shop: {
    taxPercent: 8,
    items: [
      { name: 'apple', value: 1.20 },
      { name: 'orange', value: 0.95 },
    ]
  },
  get subtotal() {
    return this.shop.items.reduce((acc, item) => acc + item.value, 0);
  },
  get tax() {
    return this.subtotal * (this.shop.taxPercent / 100)
  },
  get total() {
    return { total: this.subtotal + this.tax }
  }
})

console.log(store.subtotal) // 2.15
console.log(store.tax)      // 0.172
console.log(store.total)    // { total: 2.322 }

reselect.js

const shopItemsSelector = state => state.shop.items
const taxPercentSelector = state => state.shop.taxPercent

const subtotalSelector = createSelector(
  shopItemsSelector,
  items => items.reduce((acc, item) => acc + item.value, 0)
)

const taxSelector = createSelector(
  subtotalSelector,
  taxPercentSelector,
  (subtotal, taxPercent) => subtotal * (taxPercent / 100)
)

export const totalSelector = createSelector(
  subtotalSelector,
  taxSelector,
  (subtotal, tax) => ({ total: subtotal + tax })
)

let exampleState = {
  shop: {
    taxPercent: 8,
    items: [
      { name: 'apple', value: 1.20 },
      { name: 'orange', value: 0.95 },
    ]
  }
}

console.log(subtotalSelector(exampleState)) // 2.15
console.log(taxSelector(exampleState))      // 0.172
console.log(totalSelector(exampleState))    // { total: 2.322 }