Discussion on: Critique my JS solution to this CodeWars Kata

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const lookup = {
  'A': 'T',
  'T': 'A',
  'G': 'C',
  'C': 'G'
};

function DNAStrand(dna) {
  return [...dna].reduce((reversed, nucleotide) => {
    return reversed + lookup[nucleotide];
  }, '');
}

Defaulting to const declarations helps keep track of what's allowed to change. reduce is more appropriate when you need to accumulate results than the two-step of generating a new array and joining it. The hashtable lookup keeps the reducer body as short as possible, but there's nothing wrong with a switch per se.