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Give an example of Reselect usage?

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Let's take calculations and different amounts of a shipment order with the simplified usage of Reselect:

import { createSelector } from 'reselect'

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 }

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