VitePress

Appearance

@snailicide/build-config / utilities / Jsonify

Jsonify<T> ​

ts
type Jsonify<T> = IsAny<T> extends true ? any : T extends PositiveInfinity | NegativeInfinity ? null : T extends JsonPrimitive ? T : T extends {
  toJSON: J;
} ? () => J extends () => JsonValue ? J : Jsonify<J> : T extends Number ? number : T extends String ? string : T extends Boolean ? boolean : T extends Map<any, any> | Set<any> ? EmptyObject : T extends TypedArray ? Record<string, number> : T extends NotJsonable ? never : ... extends ... ? ... : ...;

Defined in: node_modules/.pnpm/type-fest@4.41.0/node_modules/type-fest/source/jsonify.d.ts:94

Transform a type to one that is assignable to the JsonValue type.

This includes:

  1. Transforming JSON interface to a type that is assignable to JsonValue.
  2. Transforming non-JSON value that is jsonable to a type that is assignable to JsonValue, where jsonable means the non-JSON value implements the .toJSON() method that returns a value that is assignable to JsonValue.

Type Parameters ​

Type Parameter
T

Remarks ​

An interface cannot be structurally compared to JsonValue because an interface can be re-opened to add properties that may not be satisfy JsonValue.

Examples ​

import type {Jsonify, JsonValue} from 'type-fest';

interface Geometry {
	type: 'Point' | 'Polygon';
	coordinates: [number, number];
}

const point: Geometry = {
	type: 'Point',
	coordinates: [1, 1]
};

const problemFn = (data: JsonValue) => {
	// Does something with data
};

problemFn(point); // Error: type Geometry is not assignable to parameter of type JsonValue because it is an interface

const fixedFn = <T>(data: Jsonify<T>) => {
	// Does something with data
};

fixedFn(point); // Good: point is assignable. Jsonify<T> transforms Geometry into value assignable to JsonValue
fixedFn(new Date()); // Error: As expected, Date is not assignable. Jsonify<T> cannot transforms Date into value assignable to JsonValue

Non-JSON values such as Date implement .toJSON(), so they can be transformed to a value assignable to JsonValue:

import type {Jsonify} from 'type-fest';

const time = {
	timeValue: new Date()
};

// `Jsonify<typeof time>` is equivalent to `{timeValue: string}`
const timeJson = JSON.parse(JSON.stringify(time)) as Jsonify<typeof time>;

https://github.com/Microsoft/TypeScript/issues/1897#issuecomment-710744173