Discussion on: Daily Challenge #175 - Complementary DNA

const complementaryKeys = (prev, [ a, b ]) =>
  Object.assign(prev, {
    [a]: b,
    [b]: a,
  })

const pair = (...entries) => {
  const pairs = entries.reduce(complementaryKeys, {})
  return x => pairs[x] || ''
}

const dnaPairs = pair(
  [ 'A', 'T' ],
  [ 'C', 'G' ]
)

const mapStr = fn => str =>
  str.split('')
    .map(fn)
    .join('')

const dnaStrand = mapStr(dnaPairs)