utils.js

// From https://code-boxx.com/javascript-permutations-combinations/
function allPermutations(items) {
  // allPermutations () : return a list of all possible permutations
  // Credits: https://stackoverflow.com/questions/9960908/permutations-in-javascript
  // PARAM items : array of items

  let results = []
  function permute(arr, memo) {
    var cur, memo = memo || []
    for (let i = 0; i < arr.length; i++) {
      cur = arr.splice(i, 1)
      if (arr.length === 0) {
        results.push(memo.concat(cur))
      }
      permute(arr.slice(), memo.concat(cur))
      arr.splice(i, 0, cur[0])
    }
    return results
  }
  permute(items)
  return results
}

function getCombinations(arr) {
  let combi = []
  let temp = []
  let slent = Math.pow(2, arr.length)

  for (let i = 0; i < slent; i++) {
    temp = []
    for (let j = 0; j < arr.length; j++) {
      if ((i & Math.pow(2, j))) {
        temp.push(arr[j])
      }
    }
    if (temp.length > 0) {
      combi.push(temp)
    }
  }
  return combi
}

module.exports = {
  allPermutations,
  getCombinations,
}