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

Type	Description
Any	Anything
Boolean
Const	Constant of any type
Integer	An integer type as number
Number
String
Unknown	Anything typed as unknown
Null	Only null

Supported compound types

Type	Description
AnyOf	Any type within a selection of definitions
Array	An array of a type
Enum	A string with enumerated values
Object	An object with typed properties
MergeObjects	Merge two object definitions into one object containing all the properties

Helpers

Type	Description	Example
Required	Changes the type of the schema to be required	CS.Required(CS.String(false)) === CS.String(true)
Optional	Changes the type of the schema to be optional	CS.Optional(CS.String(true)) === CS.String(false)

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.