typed-ajv

Define TypeScript types and JSON Schema schemas from the same declaration.

Getting started

Define your schema:

const cs = CS.Object({
  a: CS.String(true),
  b: CS.Number(false),
});

Get the type:

type Type = typeof cs.type; // { a: string, b?: number }

Get the json schema:

const jsonSchema = cs.getJsonSchema(); // { type: 'object', properties: [...] }

Validate your input data and type it :

if (ajv.validate(jsonSchema, inputData)) {
  const data: Type = inputData;
}

Supported primitive types

Supported compound types

Helpers

Using AnyOf with objects and removeAdditional: true

AnyOf, when ajv is configured with removeAdditional: true, doesn't behave the expected way. For example :

CS.AnyOf(
  [
    CS.Object(
      { type: CS.Enum(['car'] as const, true), wheels: CS.Number(true) },
      true,
    ),
    CS.Object(
      { type: CS.Enum(['horse'] as const, true), legs: CS.Number(true) },
      true,
    ),
  ],
  true,
);

The above schema will unexpectedly fail to validate {type: 'horse', legs: 4} because, when evaluating the 'car' option, ajv will remove all the properties except type and wheels. Thus the 'horse' option will be evaluated with the legs property removed and fail to validate.

For the above schema to work as expected, use the discriminator option:

CS.AnyOf(
  [
    CS.Object(
      { type: CS.Enum(['car'] as const, true), wheels: CS.Number(true) },
      true,
    ),
    CS.Object(
      { type: CS.Enum(['horse'] as const, true), legs: CS.Number(true) },
      true,
    ),
  ],
  true,
  { discriminator: 'type' },
);

Ajv will also need to be initialized with the discriminator: true option.