Ramda Example

adjust-price.js

// from Egghead video: https://egghead.io/lessons/javascript-handle-branching-logic-with-ramda-s-conditional-functions
import * as R from 'ramda'

const products = [
  { name: 'Jeans', price: 80, category: 'clothes' },
  { name: 'Cards', price: 5, category: 'games' },
  { name: 'iPhone', price: 649, category: 'electronics' },
  { name: 'Freakonomics', price: 30, category: 'books' },
]

const pLens = R.lensProp('price')
const applyDiscount = R.curry((perc, amt) => amt - amt * (perc / 100))

// Original (from video)
const adjustPrice = R.cond([
  [R.propEq('category', 'clothes'), R.over(pLens, applyDiscount(50))],
  [R.propEq('category', 'electronics'), R.over(pLens, applyDiscount(10))],
  [R.propEq('category', 'books'), R.over(pLens, applyDiscount(100))],
  [R.T, R.identity],
])

// Refactor (using a DISCOUNTS object)
const DISCOUNTS = {
  clothes: 50,
  electronics: 10,
  books: 100,
}
const adjustPrice2 = R.compose(
  R.cond,
  R.append([R.T, R.identity]),
  R.map(([category, discount]) => [
    R.propEq('category', category),
    R.over(pLens, applyDiscount(discount)),
  ]),
  R.toPairs
)(DISCOUNTS)

const result = R.map(adjustPrice, products)
const result2 = R.map(adjustPrice2, products)