Computes all n! permutations of an array with n items provided n < 13

perm.js

/**
* Returns an array of all possible permutations of the given array provided the arrays length is smaller then 13
* @param {Array} arr The given array to compute it's permutations. Empty array if not specified.
* @returns {Array} an array of all the possible permutations of arr
*/
function perm(arr = []) {
  if(arr.length > 12) {
    // Javascript Array max length is 2^32 - 1 but 13! > 2^32 -1
    throw new RangeError("perm() allowed max array length is 12");
  }
  if(arr.length <= 1) {
    return [arr]; // only one permutation possible
  }
  else {
    var lastItem = arr[arr.length - 1];
    var subPerms = perm(arr.slice(0, -1)); // get all permutation of n - 1 items
    var perms = [];

    subPerms.forEach((subPerm) => {
      var res_idx = 0, result = [], temp, descending = subPerm.length % 2 !== 0;
      var arr_idx = descending ? subPerm.length : 0;

      do {
        temp = subPerm.slice(0);
        temp.splice(arr_idx, 0, lastItem); // place the n-th item at each possible index for each (n - 1)-th permutation
        result[res_idx++] = temp;
      } while (descending ? arr_idx-- : arr_idx++ < subPerm.length);

      perms.push.apply(perms, result);
    });
  }

  return perms;
}

// If the file is run from the console via "node perm.js <str>" the <str> must be a JSON string that can be parsed into an array
// for example: "node perm.js '[1,2,3,4]'" will give you all permutations of the array [1,2,3,4]
// otherwise you can just require() the function as a module like so: "var perm = require('./perm.js')"

if(require.main === module) {
  var data;
  try {
    data = JSON.parse(process.argv[2]);
  }
  catch(e) {
    console.error("Argument cannot be parsed by JSON.parse");
    console.error("Reason: " + e.message);
    process.exit(1);
  }

  console.log("Permutations of ", data, ":");
  console.log(perm(data));
}
else {
  module.exports = perm;
}