arktype•3d ago

Optional required pairs?

I have a type that has all optional properties. However I want to want to make 2 options a pair - if one exists, the other is required. An example:

const props = type({
    'propA?': 'string',
    'propB?': 'string',
    'propC?': 'string'
});

// valid
props({ propA: 'test' });

// not valid - propB requires propC as well, and vice versa
props({ propB: 'test' });
props({ propC: 'test' });

// valid - both provided
props({ propB: 'test', propC: 'test' });

const props = type({
    'propA?': 'string',
    'propB?': 'string',
    'propC?': 'string'
});

// valid
props({ propA: 'test' });

// not valid - propB requires propC as well, and vice versa
props({ propB: 'test' });
props({ propC: 'test' });

// valid - both provided
props({ propB: 'test', propC: 'test' });

Is this doable? I'm using Arktype for validating incoming JSON in a server, so the use case for it is changing passwords, if you want to change your password you need to provide the current password as well, and maybe the new password a second time to confirm it

2 Replies

TizzySaurus•3d ago

One way would be to use .narrow(), which has the added benefit of being able to specify custom errors:

const props = type({ ... }).narrow((obj, ctx) =>
    "propB" in obj === "propC" in obj
        ? true
        : ctx.mustBe({
              expected:
                  "an object that either includes both or neither of 'propB' and 'propC'",
          })
);

const props = type({ ... }).narrow((obj, ctx) =>
    "propB" in obj === "propC" in obj
        ? true
        : ctx.mustBe({
              expected:
                  "an object that either includes both or neither of 'propB' and 'propC'",
          })
);

ssalbdivad•3d ago

@Tony You could use something like this:

type({
    "propA?": "string",
    "propB?": "never",
    "propC?": "never"
}).or({
    "propA?": "string",
    propB: "string",
    propC: "string"
})

type({
    "propA?": "string",
    "propB?": "never",
    "propC?": "never"
}).or({
    "propA?": "string",
    propB: "string",
    propC: "string"
})

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Optional required pairs?