Type and related utilities for dealing with nil or "falsy" values in Typescript

nil.ts

// Type and related utilities for dealing with nil or "falsy" values in Typescript
// Credits:
// • You Don't Know Javascript by Kyle Simpson [Book]
// • Javascript – The Good Parts by Douglas Crockford [Book]

/**
 * Value which behaves the same as `false` when evaluated.
 */
export type Nil = undefined | null | false | 0 | -0 | typeof NaN | "";

/**
 * Value which might be either T or `Nil`.
 */
export type Maybe<T> = T | Nil;

/**
 * Returns Boolean indicating whether `input` is `Nil`.
 */
export function isNil<T>(item?: Maybe<T>): item is Nil {
  return !Boolean(item);
}

/**
 * Returns Boolean indicating whether `input` is not `Nil`.
 */
export function isNotNil<T>(item?: Maybe<T>): item is T {
  return Boolean(item);
}