complementary-dna.js

/*
Deoxyribonucleic acid (DNA) is a chemical found in the nucleus of cells and carries the "instructions" for the development and functioning of living organisms.

If you want to know more: http://en.wikipedia.org/wiki/DNA

In DNA strings, symbols "A" and "T" are complements of each other, as "C" and "G". Your function receives one side of the DNA (string, except for Haskell); you need to return the other complementary side. DNA strand is never empty or there is no DNA at all (again, except for Haskell).

More similar exercise are found here: http://rosalind.info/problems/list-view/ (source)

Example: (input --> output)

"ATTGC" --> "TAACG"
"GTAT" --> "CATA"
*/

function DNAStrand(dna){
  let s = ''
  for(let i = 0; i < dna.length; i++){
    if (dna[i] === 'A'){
      s += 'T'
    } else if (dna[i] === 'T'){
      s += 'A'
    } else if (dna[i] === 'C'){
      s += 'G'
    } else {
      s += 'C'
    }
  }
  return s
}