ComplementaryDNA.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){
  
  return dna.split('').map(letter => 
    letter
      .replace('A', 't')
      .replace('C', 'g')
      .replace('G', 'c')                      
      .replace('T', 'a')
      .toUpperCase()
      ).join('')
    
}

//different approach

var pairs = {'A':'T','T':'A','C':'G','G':'C'};

function DNAStrand(dna){
  return dna.split('').map(function(v){ return pairs[v] }).join('');
}