gistfile1.txt

var updates = { $unset: { steak: true }, $set: { eggs: 0 } };
// Note the `runValidators` option
Breakfast.update({}, updates, { runValidators: true }, function(err) {
  console.log(err.errors['steak'].message);
  console.log(err.errors['eggs'].message);
  /*
   * The above error messages output:
   * "Path `steak` is required."
   * "Path `eggs` (0) is less than minimum allowed value (2)."
   */
});