Undefined (melange.Js.Undefined)

type +'a t

Local alias for 'a Js.undefined

module Js := Js__.Js_internal

val return : 'a -> 'a t

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

val test : 'a t -> bool

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

deprecated Use = Js.undefined directly

val testAny : 'a -> bool

since 1.6.1

Returns true if the given value is empty (undefined)

val empty : 'a t

The empty value, undefined

val getUnsafe : 'a t -> 'a

val getExn : 'a t -> 'a

val bind : 'a t -> ('a -> 'b) Js.Fn.arity1 -> 'b t

Maps the contained value using the given function

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

let maybeGreetWorld (maybeGreeting: string Js.undefined) =
  Js.Undefined.bind maybeGreeting (fun greeting -> greeting ^ " world!")

val iter : 'a t -> ('a -> unit) Js.Fn.arity1 -> unit

Iterates over the contained value with the given function

If 'a Js.undefined contains a value, that value is unwrapped and applied to the given function.

let maybeSay (maybeMessage: string Js.undefined) =
  Js.Undefined.iter maybeMessage (fun message -> Js.log message)

val fromOption : 'a option -> 'a t

Maps 'a option to 'a Js.undefined

Some a	->	return a
None	->	empty

val from_opt : 'a option -> 'a t

deprecated Use fromOption instead

val toOption : 'a t -> 'a option

Maps 'a Js.undefined to 'a option

return a	->	Some a
empty	->	None

val to_opt : 'a t -> 'a option

deprecated use toOption instead