Module Js.Undefined

Provide utilities around undefined

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

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 testAny : 'a -> bool

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

Bind 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 ~f:(fun greeting -> greeting ^ " world!")
val iter : f:('a -> unit) Js.Fn.arity1 -> 'a t -> 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 ~f:(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 toOption : 'a t -> 'a option

Maps 'a Js.undefined to 'a option

return a -> Some a
empty -> None