code: function arraySafeConcat(arr, arg) {
    var result = arrayClone(arr), len = result.length, arr2;
    arr2 = isArray(arg) ? arg : [arg];
    result.length += arr2.length;
    forEach(arr2, function(el, i) {
      result[len + i] = el;
    });
    return result;
  }
docs: Avoids issues with concat in < IE8 istanbul ignore next