@susisu/type-of-schema

Derives TypeScript type from JSON Schema

Installation

# npm
npm i @susisu/type-of-schema
# yarn
yarn add @susisu/type-of-schema
# pnpm
pnpm add @susisu/type-of-schema

Usage

import type { TypeOfSchema } from "@susisu/type-of-schema";

const schema = {
  type: "object",
  properties: {
    "a": { type: "number" },
    "b": { type: "string" },
  },
  required: ["b"],
} as const;

// T = { a?: number; b: string }
type T = TypeOfSchema<typeof schema>;

Do not forget as const in the schema declaration. Without it, you will not get the full information of the schema.

Supported Schemas

• const
• enum
• null
• number / integer
• string
• boolean
• array (items and additionalItems)
• object (properties, required, and additionalProperties)
• oneOf
• allOf

Limitations

For JSON Schema object types S and T, S extends T does not imply TypeOfSchema<S> extends TypeOfSchema<T>. In other words, a type derived from a schema can be inconsistent with what the schema actually describes. This can be observed, for example, when upcasting a schema containing required:

const schema1 = {
  type: "object",
  required: ["a"],
} as const;

// T1 = { a: Value }
type T1 = TypeOfSchema<typeof schema1>;

const schema2: {
  type: "object";
  required: ("a" | "b")[];
} = schema1;

// T2 = { a: Value; b: Value }
// but b is actually not required
type T2 = TypeOfSchema<typeof schema2>;

To avoid this, do always pass the original schema to TypeOfSchema.

License

MIT License

Author

Susisu (GitHub, Twitter)