Permutation#Generation_in_lexicographic_order

gistfile1.txt

// http://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
// callback(permutation, even)
function permutations(n, callback) {
  n >>>= 0;
  var p = n ? [] : null,
      even = true;

  for (i = 0; i < n; i++) {
    p[i] = i;
  }

  function nextPermutation() {
    var k = n - 2,
        l = n - 1, t, i;

    while (k >= 0 && p[k] > p[k + 1]) {
      k--;
    }

    if (k < 0) {
      return null;
    }

    while (p[k] > p[l]) {
      l--;
    }

    t = p[k];
    p[k] = p[l];
    p[l] = t;
    even = !even;

    // reverse
    for (i = k + 1; i < n - i + k; i++) {
      t = p[n - i + k];
      p[n - i + k] = p[i];
      p[i] = t;
      even = !even;
    }

    return p;
  }

  while (p) {
    callback(p.slice(0), even);
    p = nextPermutation();
  }
}

var s = '';
permutations(4, function (p, even) {
  s += p.join('') + ' - ' + (even ? 'even' : 'odd') +  '\n';
});
alert(s);