You are currently looking at the v6.0 - v8.2 docs (Reason v3.6 syntax edition). You can find the latest manual page here.
(These docs are equivalent to the old BuckleScript docs before the ReScript rebrand)
Interop Cheatsheet
Raw JS
Reason (Old Syntax)ML (Older Syntax)JS Output
let add = [%raw "(a, b) => a + b"];
[%%raw "const a = 1"];
Global Value
Reason (Old Syntax)ML (Older Syntax)JS Output
[@bs.val] external setTimeout: (unit => unit, int) => float = "setTimeout";
Global Module's Value
Reason (Old Syntax)ML (Older Syntax)JS Output
[@bs.val] [@bs.scope "Math"]
external random: unit => float = "random";
let someNumber = random();
[@bs.val] [@bs.scope ("window", "location", "ancestorOrigins")]
external length: int = "length";
Nullable
Reason (Old Syntax)ML (Older Syntax)JS Output
let a = Some(5); // compiles to 5
let b = None; // compiles to undefined
Handling a value that can be undefined and null, by ditching the option type and using Js.Nullable.t:
Reason (Old Syntax)ML (Older Syntax)JS Output
let jsNull = Js.Nullable.null;
let jsUndefined = Js.Nullable.undefined;
let result1: Js.Nullable.t(string) = Js.Nullable.return("hello");
let result2: Js.Nullable.t(int) = Js.Nullable.fromOption(Some(10));
let result3: option(int) = Js.Nullable.toOption(Js.Nullable.return(10));
JS Object
Function
Object Method & Chaining
Reason (Old Syntax)ML (Older Syntax)JS Output
[@bs.send] external map: (array('a), 'a => 'b) => array('b) = "map";
[@bs.send] external filter: (array('a), 'a => 'b) => array('b) = "filter";
[|1, 2, 3|]
->map(a => a + 1)
->filter(a => a mod 2 == 0)
->Js.log;
Variadic Arguments
Reason (Old Syntax)ML (Older Syntax)JS Output
[@bs.module "path"] [@bs.variadic]
external join: array(string) => string = "join";
Polymorphic Function
Reason (Old Syntax)ML (Older Syntax)JS Output
[@bs.module "Drawing"] external drawCat: unit => unit = "draw";
[@bs.module "Drawing"] external drawDog: (~giveName: string) => unit = "draw";
Reason (Old Syntax)ML (Older Syntax)JS Output
[@bs.val]
external padLeft: (
string,
[@bs.unwrap] [
| `Str(string)
| `Int(int)
])
=> string = "padLeft";
padLeft("Hello World", `Int(4));
padLeft("Hello World", `Str("Message from ReScript: "));
JS Module Interop
Dangerous Type Cast
Final escape hatch converter. Do not abuse.
Reason (Old Syntax)ML (Older Syntax)JS Output
external convertToFloat: int => float = "%identity";
let age = 10;
let gpa = 2.1 +. convertToFloat(age);
List of @bs Decorators
@bs.as@bs.get@bs.inline@bs.int@bs.meth@bs.new@bs.return@bs.scope@bs.send@bs.set@bs.string@bs.this@bs.uncurry@bs.unwrap@bs.val@bs.variadic
