http://www.freecodecamp.com/clint74 's solution for Bonfire: DNA Pairing Using functional aproach.

bonfire-dna-pairing.js

// Bonfire: DNA Pairing
// Author: @clint74
// Challenge: http://www.freecodecamp.com/challenges/bonfire-dna-pairing
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function pair(str) {
  var get_pair = {"A": "T", "T": "A", "C":"G",  "G":"C" };
  var map = Array.prototype.map;

  var dna_chain = map.call(str, function(elem){
    return [elem, get_pair[elem]];
  });
  return dna_chain;
}

pair("GCG");