function permutation(collection) {
  let current;
  let result = [];
  const currentArray = [];
  const newResultArray = [];

  if (collection.length) {
    current = collection.shift();
    result = permutation(collection);

    currentArray.push(current);

    result.map((list) => {
      newResultArray.push(list.slice(0));
      list.push(current);
    });

    result.push(currentArray);
    result = result.concat(newResultArray);
  }

  return result;
}

console.log(permutation(['a','b','c','d'])
            .join('\n'));