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.

// 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).


// Example: (input --> output)

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


function DNAStrand(dna){
  return dna.split('')
    .map( el => {
      if (el == 'A') return 'T';
      if (el == 'T') return 'A';
      if (el == 'C') return 'G';
      if (el == 'G') return 'C';
    }).join('')
}

// OR

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

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