var generatePermutations = function (items, process) {

  "use strict";

  var 

    mutableItems = items.slice(),

    isEven = function (n) {

      return (n & 1) === 0;

    },

    permute = function (itemArray, x, last) {

      if (isEven(last)) { x = 0; }

​

      var temp = itemArray[x];

      itemArray[x] = itemArray[last];

      itemArray[last] = temp;

    },

    generate = function generateNext(last, process) {

      var i;

      if (last === 0) {

        process(mutableItems);

      }

      else {

        for (i = 0; i < last; i += 1) {

          generateNext(last - 1, process);

          permute(mutableItems, i, last);

        }

        generateNext(last - 1, process);

      }

    };

  if (mutableItems.length > 0)

    generate(mutableItems.length - 1, process);

};

​

generatePermutations(["A","B"],console.log);

generatePermutations([1],console.log);

generatePermutations([],console.log);

​