type unknown - nberlette/is GitHub Wiki

@nick/is/type/unknown

IsUnknown

Signature

export type IsUnknown<A, True = true, False = false> = IsAny<
  A,
  False,
  unknowns extends A ? True : False
>;

Checks if a given type is the unknown type, resolving to True if it is, and False if not. The unknown type is the "safer" alternative to any in TypeScript, introduced in the TypeScript 3.0 release (July 2018). It is a "bottom" type, meaning it is assignable to any other type, but not vice versa. This makes it a safer choice for use in type definitions where you want to allow for any type, but still

Type Parameters
  • A
  • True (default: true)
  • False (default: false)
Category

Types

Examples

import type { IsUnknown } from "@nick/is/type";

type A = IsUnknown<unknown>; // true
type B = IsUnknown<any, "unknown", "not unknown">; // "not unknown"
import type { IsUnknown } from "@nick/is/type";

type IsNotUnknown<T> = IsUnknown<T, never, T>;

type A = IsNotUnknown<unknown>; // never
type B = IsNotUnknown<any>; // any
type C = IsNotUnknown<never>; // never
type D = IsNotUnknown<unknown[]>; // unknown[]
type E = IsNotUnknown<string>; // string
import type { IsUnknown } from "@nick/is/type";

type OmitUnknown<U, Deep extends boolean = false> = U extends
  infer T extends object ? {
    [K in keyof T as IsUnknown<T[K], never, K>]: Deep extends true
      ? OmitUnknown<T[K], true>
      : T[K];
  }
  : IsUnknown<U, never, U>;

declare const userData: OmitUnknown<{
  id: string;
  name: string;
  age: number;
  data: unknown; // <-- this will be omitted
}>;
userData;
// ^? const userData: { id: string; name: string; age: number }

OmitUnknown

Signature

export type OmitUnknown<U, Deep extends boolean = false> = U extends infer T extends object ? {
         [K in [object Object]]: Deep extends true ? OmitUnknown<T[K], true> : T[K]
    } : IsUnknown<U, never, U>;

Omit properties from an object type where the value is unknown.

This relies on the IsUnknown utility type.

Type Parameters
  • U
  • Deep extends boolean (default: false)
Category

Types

Examples

import type { OmitUnknown } from "@nick/is/type";

type A = { a: string; b: unknown; c: number };
type B = OmitUnknown<A>;
//   ^? type B = { a: string; c: number }

unknown

Signature

export type unknown =
  | {}
  | null
  | undefined;

This is an alias for the built-in unknown type in TypeScript. It is used by the IsUnknown type guard, and represents any value that is not null or undefined.

This is provided as a public export for users who want to use it in their own type definitions but without relying on built-in unknown types; it's also provided for users who are using an older version of TypeScript that does not support unknown yet.

Category

Types

unknowns

Signature

export type unknowns =
  | {}
  | null
  | undefined;

This is an alias for the built-in unknown type in TypeScript. It is used by the IsUnknown type guard, and represents any value that is not null or undefined.

This is provided as a public export for users who want to use it in their own type definitions but without relying on built-in unknown types; it's also provided for users who are using an older version of TypeScript that does not support unknown yet.

Category

Types

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