The ElixirScript.JS module has functions and macros that help with interacting with JavaScript. These mostly correspond to JavaScript keywords that may be useful.

# Calling the JavaScript Debugger
ElixirScript.JS.debugger()

# Getting the type of a value
ElixirScript.JS.typeof(my_value)

ElixirScript calls JavaScript modules through a Foreign Function Interface (FFI). A foreign module is defined by creating a new module and adding use ElixirScript.FFI to it.

Here is an example of a foreign module for a JSON module

defmodule MyApp.JSON do
  use ElixirScript.FFI

  foreign stringify(map)
  foreign parse(string)
end

Foreign modules map to JavaScript files that export functions defined with the foreign macro. ElixirScript expects JavaScript modules to be in the priv/elixir_script directory. These modules are copied to the output directory upon compilation.

For our example, a JavaScript file must be placed at priv/elixir_script/my_app/json.js.

It looks like this

export default {
  stringify: JSON.stringify,
  parse: JSON.parse
}

In order to start an ElixirScript application, you must first import it using whichever JavaScript module system you are using and then call Elixir.start

# Our ElixirScript module

defmodule Main do
  def start(:normal, args) do
    args
  end
end

//ES module example
import Elixir from './Elixir.App'
Elixir.start(Elixir.Main, [1, 2, 3])

In the above example, we have an ElixirScript module, Main with a start/2 function. This function is the entry point into your ElixirScript application. when we call Elixir.start, we give it this module's name (All modules when compiled begin with Elixir.) and a list of the initial args.

If you want to use an ElixirScript module inside of your JavaScript code, you can do so using Elixir.load.

# Our ElixirScript module

defmodule MyModule do
  def hi() do
    "hello"
  end
end

const MyModule = Elixir.load(Elixir.MyModule);
MyModule.hi()