Initial Rules

When assigning the validation rules, you will likely want to start with the initial rules.

Required

The field under validation must be present in the input data and not empty.

const rules = {
 foo: "required",
};

Sometimes

Run validation checks against a field only if that field is present in the data being validated.

const rules = {
 foo: "sometimes",
};

Nullable

The field under validation may be null.

const rules = {
 foo: "nullable",
};