Docs / API / Js / Undefined

Undefined

Provides functionality for dealing with the Js.undefined<'a> type

t

RESCRIPT
type t<'a> = Js.undefined<'a>

Local alias for Js.undefined<'a>

return

RESCRIPT
let return: 'a => t<'a>

Constructs a value of Js.undefined<'a> containing a value of 'a.

test

Deprecated

Use = Js.undefined directly

RESCRIPT
let test: t<'a> => bool

Returns true if the given value is empty (undefined), false otherwise.

testAny

RESCRIPT
let testAny: 'a => bool

Returns true if the given value is empty (undefined).

since 1.6.1

empty

RESCRIPT
let empty: t<'a>

The empty value, undefined

getUnsafe

RESCRIPT
let getUnsafe: t<'a> => 'a

getExn

RESCRIPT
let getExn: t<'a> => 'a

bind

RESCRIPT
let bind: (t<'a>, 'a => 'b) => t<'b>

Maps the contained value using the given function. If Js.undefined<'a> contains a value, that value is unwrapped, mapped to a 'b using the given function a' => 'b, then wrapped back up and returned as Js.undefined<'b>.

Examples

RESCRIPT
let maybeGreetWorld = (maybeGreeting: Js.undefined<string>) =>
  Js.Undefined.bind(maybeGreeting, (. greeting) => greeting ++ " world!")

iter

RESCRIPT
let iter: (t<'a>, 'a => unit) => unit

Iterates over the contained value with the given function. If Js.undefined<'a> contains a value, that value is unwrapped and applied to the given function.

Examples

RESCRIPT
let maybeSay = (maybeMessage: Js.undefined<string>) =>
  Js.Undefined.iter(maybeMessage, (. message) => Js.log(message))

fromOption

RESCRIPT
let fromOption: option<'a> => t<'a>

Maps option<'a> to Js.undefined<'a>. Some(a) => a None => empty

from_opt

Deprecated

Use fromOption instead

RESCRIPT
let from_opt: option<'a> => t<'a>

toOption

RESCRIPT
let toOption: t<'a> => option<'a>

Maps Js.undefined<'a> to option<'a> a => Some(a) empty => None

to_opt

Deprecated

use toOption instead

RESCRIPT
let to_opt: t<'a> => option<'a>