Find all permutations of a string using base case & build approach. See: https://en.wikipedia.org/wiki/Permutation

permutations.js

//
// Find all permutations of a string using base case & build approach
//
// See: https://en.wikipedia.org/wiki/Permutation
//
'use strict';

if (!String.prototype.splice) {
  /**
   * @method - Add "splice" to String
   */
  String.prototype.splice = function(start, deleteCount, insert) {
    if (start > this.length) {
      start = this.length;
    }
    if (!insert) {
      insert = '';
    }
    return this.slice(0, start) + insert + this.slice(start + deleteCount);
  };
}

/**
 * Find all permutations of a string
 *
 * @param {string} input - The string input
 * @return {array} - The list of permutations
 */
const permutations = function(input) {
  // if input is not a string, throw error
  if (typeof input !== 'string') {
    throw new Error('Input was invalid');
  }
  // use base case & build approach
  let perms = [''];
  for (let i = 0; i < input.length; i++) {
    let char = input.charAt(i);
    let permsLen = perms.length;
    // loop through each existing permuation
    for (let j = 0; j < permsLen; j++) {
      // add the input[i] character at each point in the string
      for (let k = 0; k <= perms[j].length; k++) {
        perms.push(perms[j].splice(k, 0, char));
      }
    }
  }
  // we're only interested in permutations of the full string length
  // also, sort the list, since we don't really care about performance here
  return perms.filter(perm => perm.length === input.length).sort();
};

//
// For usage with Node.js
//
if (typeof window === 'undefined' && typeof global === 'object') {
  // if no args provided, print usage
  if (process.argv.length < 3) {
    return console.log('Usage: node permutations.js {string}');
  }

  // get string from args
  const str = process.argv[2];

  // return all permutations
  return console.log(permutations(str));
}