var minWindow = function (s, t) {
  var result = '';

  var map = {};
  t.split('').forEach(item => map[item] = (map[item] || 0)   1);

  var count = Object.keys(map).length;

  var l = 0, r = -1;
  while (r < s.length) {
    if (count == 0) {
      if (!result || r - l   1 < result.length) {
        result = s.slice(l, r   1);
      }
      if (map[s[l]] !== undefined) {
        map[s[l]]  ;
      }
      if (map[s[l]] > 0) {
        count  ;
      }
      l  ;
    } else {
      r  ;
      if (map[s[r]] !== undefined) {
        map[s[r]]--;
      }
      if (map[s[r]] == 0) {
        count--;
      }
    }
  }
  return result;
};