https://adrianmejia.com/most-popular-algorithms-time-complexity-every-programmer-should-know-free-online-tutorial-course/#Permutations

permutations.js

function getPermutations(string, prefix = '') {
  if(string.length <= 1) {
    return [prefix + string];
  }

  return Array.from(string).reduce((result, char, index) => {
    const reminder = string.slice(0, index) + string.slice(index+1);
    result = result.concat(getPermutations(reminder, prefix + char));
    return result;
  }, []);
}