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2.0.0 • Public • Published


Bindings for mounting and interacting with Elm applications in Reason.


Writing web applications in Elm is nice. It's type system and enforced architecture are just a couple of the really cool things that it offers. The Elm ecosystem is pretty small compared to the Javascript(JS) ecosystem, and this is a draw back when coming from the world of JS. Interop with JS is possible, but it requires writing regular JS code, which has none of Elm's safety. This is where Reason enters the picture. Reason can communicate more direclty with JS with much more type safety than vanilla JS. The possibility of writing an Elm app and handling JS interop with Reason is pretty powerful. Having access to the entire JS ecosytem in a (more) typesafe way is pretty exciting, so bs-elm was created.

Getting Started

  • Install
    • With yarn: yarn add bs-elm
    • With npm: npm install --save bs-elm
  • Add bs-elm as a dependency in bsconfig.json
  "bs-dependencies": ["bs-elm"]
  • Use the Elm module in reason
module R = Belt.Result;

external elmProgram : Elm.elmProgram = "path/to/App.elm";

let instance = Elm.mount(
  ~moduleName="App", /* Defaults to "Main" */
  elmProgram /* Must be last arguement */

switch instance {
| R.Ok(i) => Js.log("Elm is running.")
| R.Error(errorMessage) => Js.log(errorMessage)

To import Elm directly in Reason ->

Checkout this example that uses flags and ports!


If you have any suggestions or run into any bugs, please open an issue!


  • Make interacting with ports nicer

    • Convert Js.t objects to OCaml records?
    • Subscribe to ports in a pipeline style?

Change log

v1.0.2 ->

  • Compile reason modules in-source

v1.0.1 ->

  • Upgrade to bs-platform@3.0.0 (No change in the generated code)
  • Generate files with the suffix .bs.js instead of .js
  • NOTE: If using webpack this, changes how the project must be built. Please refer to jaredramirez/bs-elm-example for an example.

v1.0.0 ->

  • Rename project to bs-elm
  • Changed exported module from ReasonElm to Elm
  • Changed export port types to elmOutPort -> portToElm and elmInPort -> portFromElm


npm i bs-elm

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