option.ts

option.ts

Option ~Monad for typescript

option.ts can be used with either javascript or typescript 2.0.
This Option wrapper is mostly meant to be used at call sites, where you want to create and transform optional value expressions. The advantage of only using it there, is that you keep neat, non wrapped JSON structures as your data.

API

• Option()
• Option.all()
• None
• map
• flatMap
• filter
• orElse
• [Reading the Option value](#Reading the Option value)
• isDefined
• getOrElse

Creating an Option

Option(x)

Creates an Option from a value. If the value is null or undefined, it will create a None, else a Some.

const some = Option(33) // some === Some(33)
const none = Option(null) // none === None

Option.all(...optionsOrValues, transform)

Creates a new Option holding the computation of the passed Options if they were all Some or plain defined instances, else returns None

const some = Option.all(
  Option(10), 20, Option(5),
  (a, b, c) => a + b + c
)
// some === Some(35)

const none = Option.all(
  Option(10), None, Option(5),
  (a, b, c) => a + b + c
)
// none === None

None

The Option constant representing no value. Note: Some can not be imported as it would result in unsafe Option creations (e.g Some containing null/undefined). Instead, use Option(myValue).

import { None } from 'option.ts'

Transforming an Option

map

Maps the value contained in this Some, else returns None. Depending on the map function return value, a Some could be tranformed into a None, as a Some will never contain a null or undefined value.

const some = Option(33).map(x => x * 2)
// some === Some(66)

flatMap

Maps the value contained in this Some to a new Option, else returns None.

const some = Option(33).flatMap(_ => Option(44))
// some === Some(44)

filter

If this Option is a Some and the predicate returns true, keep that Some. In all other cases, return None.

const some = Option(33).filter(x => x > 32)
// some === Some(33)

orElse

Returns this Option unless it's a None, in which case the provided alternative is returned.

const some = Option(null).orElse(() => Option(33))
// some === Some(33)

Misc

Accessing the underlying value of the Option

Options are simple functions, call it to access the underlying value. Some instances return their value, whereas None returns undefined

const value = Option(33)()
// value === 33

isDefined

Returns whether this Option has a defined value (i.e, it's a Some(value))

getOrElse

Returns this Option's value if it's a Some, else return the provided alternative

const value = Option(undefined).getOrElse(33)

// value === 33