Types

Things that should exist in type-fest, but don't (yet).

Some types are copy-pasted from type-fest, because:

1. To not introduce (another) dependency of this 0-dep lib
2. To avoid multiple type-fest versions conflicts (that happened many times in the past)

StringMap

const m: StringMap = { a: 'a' }
// Same as:
// const m: { [a: string]: string | undefined }

const m: StringMap<number> = { a: 5 }
// Same as:
// const m: { [a: string]: number | undefined }

The | undefined part is important!

It allows to set undefined values to StringMap, e.g:

m.name = name1 // where `name1` can be undefined

Mapper

export type Mapper<IN = any, OUT = any> = (input: IN, index: number) => OUT

AsyncMapper

export type AsyncMapper<IN = any, OUT = any> = (input: IN, index: number) => OUT | PromiseLike<OUT>

Predicate

export type Predicate<T> = (item: T, index: number) => boolean

Async Predicate

export type AsyncPredicate<T> = (item: T, index: number) => boolean | PromiseLike<boolean>

_passthroughPredicate

Predicate that passes everything (returns true for every item).

_passthroughPredicate(anything) // true
  [(1, 2, 3)].filter(_passthroughPredicate)
// [1, 2, 3]

_passNothingPredicate

Predicate that passes nothing (returns false for every item).

_passNothingPredicate(anything) // false
  [(1, 2, 3)].filter(_passNothingPredicate)
// []

_noop

Function that takes any arguments and returns undefined. Literally does nothing.

Can be useful to replace some real world functions with mocks.

element.click = _noop

Merge

ReadonlyDeep

Promisable

PromiseValue