code: function pick(obj, select) {
    var result = {};
    if (typeof select === 'string') {
      select = [].slice.call(arguments, 1);
    }
    var len = select.length;
    for (var i = 0; i < len; i++) {
      var key = select[i];
      if (key in obj) {
        result[key] = obj[key];
      }
    }
    return result;
  }
docs: /*
  var obj = {a: 3, b: 5, c: 9};
  pick(obj, ['a', 'c']); // {a: 3, c: 9}
  pick(obj, 'a', 'c'); // {a: 3, c: 9}
  pick(obj, ['a', 'b', 'd']); // {a: 3, b: 5}
  pick(obj, ['a', 'a']); // {a: 3}