isNonNullable.ts22 lines · main

1	export type Maybe<T> = T | null | undefined
2
3	/**
4	* Used to test whether a `Maybe` typed value is `null` or `undefined`.
5	*
6	* When called, the given value's type is narrowed to `NonNullable<T>`.
7	*
8	* ### Example Usage:
9	*
10	* ```ts
11	* const fn = (str: Maybe<string>) => {
12	* if (!isNonNullable(str)) {
13	* // typeof str = null | undefined
14	* // ...
15	* }
16	* // typeof str = string
17	* // ...
18	* }
19	* ```
20	*/
21	export const isNonNullable = <T extends Maybe<unknown>>(val?: T): val is NonNullable<T> =>
22	typeof val !== `undefined` && val !== null