array.js

const numbers = [1, 2, 3, 4, 5, 6];
const increment = numbers => numbers.map(number => number + 1)
const fetchEven = numbers => numbers.filter(number => number % 2 === 0)
const toString = numbers => numbers.map(number => number.toString())
const concat = strings => strings.reduce((result, string) => result += string, '')
const compose = (...fns) => ((arg) => fns.reduce((result, fn) => fn(result), arg))

console.log(concat(toString(fetchEven(increment(numbers)))))
console.log(compose(increment, fetchEven, toString, concat)(numbers))