Option

Option type for Typescript based on the Scala Option type

If you're already familliar with type Option type, this should work more or less like you would expect it to.

Issues and PRs are welcome if you find any bugs in the code.

Install

yarn add @alanqthomas/option

npm install @alanqthomas/option

Development

Test with watch: yarn test

Test once: yarn testOnce

Build Typescript: yarn build

Generate Docs: yarn docs

Examples

See the TypeDoc documentation for more specific type info.

Import

import { Option, Some, None } from '@alanqthomas/option'

Constructors

Convenience methods to create new options without using new. This also means that the real classes behind them are suffixed with an _, e.g. Option_.

const someVal = Option(42)
              = Some(42)
const noneVal = None
              = Option(null)
              = Option(undefined)
              = Option.empty<WhateverType>()

Option.empty is useful is you need a None that conforms to a certain type.

Let's use these values for our examples (A will be number):

// Option<Int>
const some = Some(42)
const none = Option.empty<number>()

isEmpty(): boolean

some.isEmpty() // false
none.isEmpty() // true

isDefined(): boolean

some.isDefined() // true
none.isDefined() // false

nonEmpty(): boolean (alias for isDefined)

some.isDefined() // true
none.isDefined() // false

get(): A

some.get() // 42
none.get() // throws ReferenceError!!

getOrElse(e: A): Option<A>

some.getOrElse(0) // 42
none.getOrElse(0) // 0

orElse(alt: Option<A>): Option<A>

some.orElse(Some(0)) // Some(42)
none.orElse(Some(0)) // Some(0)

map<B>(f: (a: A) => B): Option<B>

some.map(x => x + 2) // Some(44)
none.map(x => x + 2) // None

flatMap<B extends NonEmpty>(f: (a: A) => Option<B>): Option<B>

some.flatMap(x => Some(x + 2)) // Some(44)
none.flatMap(x => Some(x + 2)) // None

NonEmpty is a type alias for a non-null, non-undefined value type NonEmpty = string | number | boolean | symbol | object

fold<B>(b: B, f: (a: A) => B): B

some.fold(0, x => x + 2) // 44
none.fold(0, x => x + 2) // 0

filter(p: (a: A) => boolean): Option<A>

some.filter(x => x === 42) // Some(42)
none.filter(x => x === 42) // None

filterNot(p: (a: A) => boolean): Option<A>

some.filterNot(x => x === 0) // Some(42)
none.filterNot(x => x === 0) // None

contains(elem: A): boolean

some.contains(42) // true
none.contains(42) // false

exists(p: (a: A) => boolean): boolean

some.exists(x => x === 42) // true
none.exists(x => x === 42) // false

forall(p: (a: A) => boolean): boolean

some.forall(x => x === 42) // true
none.forall(x => x === 42) // true

foreach<B>(f: (a: A) => B): void

some.foreach(x => console.log(x)) // prints 42
none.foreach(x => console.log(x)) // doesn't print

toArray(): Array<A>

some.toArray() // [42]
none.toArray() // []

match<B, C>(matches): B | C

matches is an object of shape:

matches: {
  none: () => C,
  some: (a: A) => B
}

Of course, order doesn't matter in an object, so you can put in the some or none function in the order you want

some.match({
  some: x => x + 2,
  none: () => 0
}) // 44

none.match({
  some: x => x + 2,
  none: () => 0
}) // 0