Update documentation for FFI module

bryanjos · bryanjos · commit f4d45872c018 · 2017-07-13T22:26:01.000-05:00
diff --git a/lib/elixir_script/ffi.ex b/lib/elixir_script/ffi.ex
@@ -1,6 +1,35 @@
 defmodule ElixirScript.FFI do
   @moduledoc """
   The foreign function interface for interoperability with JavaScript.
+
+  Define foreign modules with `use ElixirScript.FFI`.
+  Next to define functions for the foreign module, use the `foreign` macro.
+
+  Here is an example of a foreign module for a JSON module
+
+  ```elixir
+  defmodule MyApp.JSON do
+    use ElixirScript.FFI
+
+    foreign stringify(map)
+    foreign parse(string)
+  end
+  ```
+
+  Foreign modules must have an equivalent JavaScript module.
+  ElixirScript expects JavaScript modules to be in the `priv/elixir_script` directory.
+  These modules will be copied to the output directory upon compilation.
+
+  In the example, a JavaScript file must be at `priv/elixir_script/my_app/json.js`.
+  It looks like this
+  ```javascript
+  export default {
+    stringify: JSON.stringify,
+    parse: JSON.parse
+  }
+  ```
+
+  The JavaScript module must export a default object with the foreign functions defined in the Elixir module
   """
 
   defmacro __using__(opts) do
diff --git a/test/support/main.ex b/test/support/main.ex
@@ -1,7 +1,5 @@
 defmodule Main do
   def start(:normal, [callback]) do
     callback.("started")
-    Agent.start(fn() -> nil end)
-    Data.JSON.stringify(%{})
   end
 end
