Option, Null, Undefined

option

• Use option type to deal with nonexistent value
• Use mostly Js.Belt.Option, or Js.Option

Interoperate with JS undefined and null

• Never, EVER, pass a nested option value (e.g. Some(Some(Some(5)))) into the JS side.

• Never, EVER, annotate a value coming from JS as option<'a>. Always give the concrete, non-polymorphic type.

• Use Js.Nullable.null or Js.Nullable.undefined if expecting null or undefined from JS side

// consuming JS null 
@module("MyConstant") external myId: Js.Nullable.t<string> = "myId"

// passing Nullable from Rescript to JS
@module("MyIdValidator") external validate: Js.Nullable.t<string> => bool = "validate"
let personId: Js.Nullable.t<string> = Js.Nullable.return("abc123")
let result = validate(personId)