http://www.freecodecamp.com/patrickcurl 's solution for Bonfire: DNA Pairing

bonfire-dna-pairing.js

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

function pair(str) {
 var dna = str.split("");
 var pairs = [];
 dna.forEach(function(x){
   if(x === "G"){ pairs.push(["G","C"]);}
   if(x === "C"){ pairs.push(["C","G"]);}
   if(x === "T"){ pairs.push(["T","A"]);}
   if(x === "A"){ pairs.push(["A","T"]);}
 });
 return pairs;
}

pair("GCG");