Undefined

t

type t('a) = Js.undefined('a);

Local alias for 'a Js.undefined.

return

let return: 'a => t('a);

Constructs a value of Js.undefined('a) containing a value of 'a.

test

let test: t('a) => bool;

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

testAny

let testAny: 'a => bool;

Since 1.6.1 Returns true if the given value is empty (undefined).

empty

let empty: t('a);

The empty value, undefined.

getUnsafe

let getUnsafe: t('a) => 'a;

getExn

let getExn: t('a) => 'a;

bind

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).

RE
let maybeGreetWorld = (maybeGreeting: Js.undefined(string)) =>
  Js.Undefined.bind(maybeGreeting, [@bs] greeting => greeting ++ " world!");

iter

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.

RE
let maybeSay = (maybeMessage: Js.undefined(string)) =>
  Js.Undefined.iter(maybeMessage, [@bs] message => Js.log(message));

fromOption

let fromOption: option('a) => t('a);

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

from_opt

let from_opt: option('a) => t('a);

toOption

let toOption: t('a) => option('a);

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

to_opt

let to_opt: t('a) => option('a);