Js
The Js module mostly contains ReScript bindings to _standard JavaScript APIs_ like [console.log](https://developer.mozilla.org/en-US/docs/Web/API/Console/log), or the JavaScript [String](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String), [Date](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date), and [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) classes. It is meant as a zero-abstraction interop layer and directly exposes JavaScript functions as they are. If you can find your API in this module, prefer this over an equivalent Belt helper. For example, prefer [Js.Array2](js/array-2) over [Belt.Array](belt/array) ## Argument Order For historical reasons, some APIs in the Js namespace (e.g. [Js.String](js/string)) are using the data-last argument order whereas others (e.g. [Js.Date](js/date)) are using data-first. For more information about these argument orders and the trade-offs between them, see [this blog post](https://www.javierchavarri.com/data-first-and-data-last-a-comparison/). _Eventually, all modules in the Js namespace are going to be migrated to data-first though._ In the meantime, there are several options for dealing with the data-last APIs: ```rescript /* Js.String (data-last API used with pipe last operator) */ Js.log("2019-11-10" |> Js.String.split("-")) Js.log("ReScript" |> Js.String.startsWith("Re")) /* Js.String (data-last API used with pipe first operator) */ Js.log("2019-11-10"->Js.String.split("-", _)) Js.log("ReScript"->Js.String.startsWith("Re", _)) /* Js.String (data-last API used without any piping) */ Js.log(Js.String.split("-", "2019-11-10")) Js.log(Js.String.startsWith("Re", "ReScript")) ``` ## Js.Xxx2 Modules Prefer `Js.Array2` over `Js.Array`, `Js.String2` over `Js.String`, etc. The latters are old modules.
t
type t<'a> = 'a constraint 'a = {..}JS object type
null
type null<'a> = Value('a) | NullNullable value of this type can be either null or 'a. This type is equivalent to Js.Null.t.
undefined
type undefined<+'a>A value of this type can be either undefined or 'a. This type is equivalent to Js.Undefined.t.
nullable
type nullable<'a> = Value('a) | Null | Undefinednull_undefined
type null_undefined<'a> = nullable<'a>toOption
let toOption: nullable<'a> => option<'a>undefinedToOption
let undefinedToOption: undefined<'a> => option<'a>nullToOption
let nullToOption: null<'a> => option<'a>isNullable
let isNullable: nullable<'a> => boolimport
let import: 'a => promise<'a>testAny
let testAny: 'a => boolThe same as {!test} except that it is more permissive on the types of input
promise
type promise<+'a, +'e>The promise type, defined here for interoperation across packages.
null
let null: null<'a>The same as empty in `Js.Null`. Compiles to `null`.
undefined
let undefined: undefined<'a>The same as empty `Js.Undefined`. Compiles to `undefined`.
typeof
let typeof: 'a => string`typeof x` will be compiled as `typeof x` in JS. Please consider functions in `Js.Types` for a type safe way of reflection.
log
let log: 'a => unitEquivalent to console.log any value.
log2
let log2: ('a, 'b) => unitlog3
let log3: ('a, 'b, 'c) => unitlog4
let log4: ('a, 'b, 'c, 'd) => unitlogMany
let logMany: array<'a> => unitA convenience function to console.log more than 4 arguments
eqNull
let eqNull: ('a, null<'a>) => booleqUndefined
let eqUndefined: ('a, undefined<'a>) => booleqNullable
let eqNullable: ('a, nullable<'a>) => boolunsafe_lt
let unsafe_lt: ('a, 'a) => bool`unsafe_lt(a, b)` will be compiled as `a < b`. It is marked as unsafe, since it is impossible to give a proper semantics for comparision which applies to any type
unsafe_le
let unsafe_le: ('a, 'a) => bool`unsafe_le(a, b) will be compiled as `a <= b`. See also `Js.unsafe_lt`.
unsafe_gt
let unsafe_gt: ('a, 'a) => bool`unsafe_gt(a, b)` will be compiled as `a > b`. See also `Js.unsafe_lt`.
unsafe_ge
let unsafe_ge: ('a, 'a) => bool`unsafe_ge(a, b)` will be compiled as `a >= b`. See also `Js.unsafe_lt`.
