0.3.3 • Public • Published

This package is a fork of bs-elm-es6, which is still being actively maintained. However, this project uses the latest ReScript syntax. If you are familiar with the new syntax, you will probably be most comfortable with this project.


a standalone package for interoperation between Elm and ReScript.


This is a standalone binding for Elm 0.19 ports. It has no dependencies and can be used without a bundler. It is meant to be highly idiomatic to JavaScript developers.


npm install res-elm in your console and then add "res-elm" to your bs-dependencies.


  1. (Optional) Expose the module in your Index.res, like so:
open Elm;
  1. Define your ports type as a record, where each field is either a sendable of a type or a subscribable of a type. For example:
type ports = 
    toElm: Elm.sendable<string>,
    fromElm: Elm.subscribable<string>
  1. Get your target node and initialize your app. For example:
    @val @scope ("document")
    external getElementById: string => Dom.element = "getElementById";
    let app:<ports> = 
      Elm.Main.initWithOptions({ node: Some(getElementById("elm-target")),
                                 flags: None
  1. Use your ports. There are two ways to do this.

The ReScript-y Way to use ports.

res-elm exposes methods Elm.send('model, sendable<'model>) and Elm.subscribe(('model => unit), subscribable<'model>).

You can pipe into these methods like so:

app.ports.toElm -> Elm.send("Hello, from ReScript.");
app.ports.fromElm -> Elm.subscribe(str => Js.log(str));

I imagine this is the primary way most users will interact with this package.

The JavaScript-y Way to use ports.

res-elm also exposes a less-idiomatic-to-ReScript way to interact with Elm ports. That is, sendable<'model> and subscribable<'model> are both records with a function-valued field.

That is, you can literally call the object method directly in ReScript like:

app.ports.toElm.send("Hello, from ReScript");

This is kind of a cringe-y hack and I don't imagine it will be widely used, but it may be useful if you're coming from the JavaScript/Elm world or if you want a faster refactor from JavaScript to ReScript. (Plus, I really just wanted to see if something like this would work, and it does.)


There's a fully functioning, minimal example at which includes one incoming and one outgoing port. It is explained further in the article I wrote about it.

Let me know if you have any questions.

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