type undefined - nberlette/is GitHub Wiki

@nick/is/type/undefined

IsUndefined

Signature

export type IsUndefined<T, True = true, False = false> = [T] extends [never]
  ? False
  : [T] extends [undefined] ? [void] extends [T] ? False : True
  : False;

Checks if the type T is specifically undefined, returning True if it is, and False if not. This does not recognize void as undefined.

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

Types

Examples

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

type A = IsUndefined<undefined>; // true
type B = IsUndefined<null>; // false
type C = IsUndefined<never>; // false
type D = IsUndefined<void>; // false

OmitUndefined

Signature

export type OmitUndefined<T, Deep extends boolean = false> = T extends object ? {
         [K in [object Object]]: Deep extends true ? OmitUndefined<T[K], Deep> : T[K]
    } : T;

Omit properties from an object type where the value is undefined. This relies on the IsNever utility type.

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

Types

Examples

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

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