Day 1 - Advent of .js

const numbers =
  input
    .trim()
    .split("\n")
    .map(Number)
        
const sums =
  numbers
    .flatMap(n =>
      numbers.map(k => n + k))

const floor =
  Math.floor

const length =
  numbers.length

const productAtIndex =
  i =>
    numbers[floor(i / length)]
      * numbers[i % length]

const answer =
  sums
    .reduce((answer, sum, i) =>
      Math.max(answer, sum == 2020 ? productAtIndex(i) : 0),
      0
    )

answer


// Part 2 ---

const numbers =
  input
    .trim()
    .split("\n")
    .map(Number)

const sums =
  numbers
    .flatMap(n => numbers.map(k => r => n + k + r))
    .flatMap(f => numbers.map(f))

const floor =
  Math.floor

const length =
  numbers.length

const productAtIndex =
  i =>
    numbers[i % length]
    * numbers[floor(i / length) % length]
        * numbers[floor(i / length / length) % length]

const answer =
  sums
    .reduce((answer, sum, i) =>
      Math.max(answer, sum == 2020 ? productAtIndex(i) : 0),
      0
    )

answer