ElixirScript 0.30.0 Released | Elixirscript

August 15, 2017

ElixirScript 0.30.0 Released

ElixirScript 0.30 is a large release with lots of changes. It includes a rewrite of the compiler, a change in JavaScript interoperability and much more. This is also the first version to require Erlang 20 and Elixir 1.5, compiled with Erlang 20. ElixirScript can compile your Elixir code and dependencies into JavaScript, with some limitations. These changes make this the best release of ElixirScript so far! This is a great point to give ElixirScript a try for yourself. This post will describe the major changes.

Foreign Function Interface (FFI)

JavaScript interoperability has changed. ElixirScript now interacts with JavaScript using an FFI. This means there is a stricter barrier between Elixir and JavaScript. The FFI allows the ability to make packages designed to work with ElixirScript. Another benefit is that there are far fewer warnings during compilation time. As an example let’s create an FFI module for some HTTP specific functions we want to use from JavaScript.

An FFI module has 2 parts: the Elixir module and the corresponding JavaScript module.

Our Elixir module, MyApp.Http

defmodule MyApp.Http do
  use ElixirScript.FFI

  defexternal get(url)
  defexternal post(url, body)

Our JavaScript module

function get(url) {
 // Implementation goes here
function post(url, body) {
 // Implementation goes here

export default {

ElixirScript depends on the JavaScript module being at a certain path. It will look for the JavaScript module either at priv/elixir_script/my_app/http.js or priv/elixir_script/my_app.http.js. If your code uses the FFI module, during compilation ElixirScript copies the js file along side the compilation output. The generated output imports the js file. The JavaScript module must be an ES module that exports a default object containing the functions you want to use.

With the above in place, you can call functions on MyApp.Http as you would any other Elixir module.

For more information, check the documentation for ElixirScript.FFI.


ElixirScript can compile your project’s dependencies to JavaScript. This means you can use many of the packages available in Hex. It is also possible to create ElixirScript-specific packages. These are normal mix projects which may or may not have FFI modules with their corresponding JavaScript files.

If creating a Hex package for ElixirScript, please prepend elixir_script to your package name. This is so that it is clear your package is to be use with ElixirScript. For example, a React package would be named elixir_script_react. Here is an example.

A Call to Arms

Calls to Erlang functions that the Elixir standard library make have to be reimplemented in JavaScript. There are many that are implemented, but there are more that need to be. This effects the availability of some Elixir standard library calls. A major contribution to ElixirScript would be to help with an implementation of an Erlang function that is blocking the use of an Elixir function you want to use!

Breaking Changes

ElixirScript now only works as a mix compiler. This means there will no longer be an escript for download and plugins for Brunch and Webpack will no longer work with this and future versions.

ElixirScript now only supports output of ES modules.


receive is still not supported. When ElixirScript encounters a receive call during compilation, the compiler will show a warning, but will continue. During runtime these calls will throw an error. With receive not yet supported, this also means most of OTP is not supported as well.


Finally, I want to give a great big thanks to the Elixir Core Team! Thanks for making the updates in Erlang and Elixir that allowed ElixirScript’s progress to continue. And thank you for being available to answer questions and to give great advice!

For more information regarding changes, please check the changelog.

For more on getting started with ElixirScript, check the ElixirScript documentation

For more on FFI, and other things, check out the FFI documentation

For more on JavaScript Interoperability, check out the JavaScript interoperability documentation

For an example of an ElixirScript app, check out the Todo Example App