transducer

const { map, filter, compose, transduce } = require('ramda'); // utils const timeIt = (label, fn) => { console.time(label); fn(); console.timeEnd(label); }; const getRange = n => [...Array(n).keys()] // data const users = getRange(1000000).map((_, index) => ({ registered: index % 2 === 0, discount: 1, })) // helpers const isRegistered = user => user.registered; // predicate const getDiscount = user => user.discount; // transform // transduce reverse the compose hence we reversed the order const getDiscountForRegisteredUsers = compose(filter(isRegistered), map(getDiscount)); const totalDiscountReducer = (totalDiscount, discount) => totalDiscount + discount; // reducer // elegant and efficient way to get total discount const getTotalDiscountForRegisteredUsers = () => transduce( getDiscountForRegisteredUsers, totalDiscountReducer, 0, users ) // elegant way to get total discount const getTotalDiscountForRegisteredUsersElegantly = () => users .filter(isRegistered) .map(getDiscount) .reduce(totalDiscountReducer, 0) // efficient way to get total discount const getTotalDiscountForRegisteredUsersEfficiently = () => { let totalDiscount = 0; users.forEach(user => { if(user.registered) totalDiscount += user.discount; }) return totalDiscount; } timeIt('Loop(Efficient)', getTotalDiscountForRegisteredUsersEfficiently) timeIt('Chaining(Elegant)', getTotalDiscountForRegisteredUsersElegantly) timeIt('Transduce(Efficient and Elegant)', getTotalDiscountForRegisteredUsers)