NodeJS

Provides an Elixir API for calling Node.js functions.

Documentation

The docs can be found at https://hexdocs.pm/nodejs.

Prerequisites

• Elixir >= 1.7
• NodeJS >= 10

Installation

def deps do
  [
    {:nodejs, "~> 2.0"}
  ]
end

Starting the service

Add NodeJS to your Supervisor as a child, pointing the required path option at the directory containing your JavaScript modules.

supervisor(NodeJS, [[path: "/node_app_root", pool_size: 4]])

Calling JavaScript module functions with NodeJS.call(module, args \\ []).

If the module exports a function directly, like this:

module.exports = (x) => x

You can call it like this:

NodeJS.call("echo", ["hello"]) #=> {:ok, "hello"}

There is also a call! form that throws on error instead of returning a tuple:

NodeJS.call!("echo", ["hello"]) #=> "hello"

If the module exports an object with named functions like:

exports.add = (a, b) => a + b
exports.sub = (a, b) => a - b

You can call them like this:

NodeJS.call({"math", :add}, [1, 2]) # => {:ok, 3}
NodeJS.call({"math", :sub}, [1, 2]) # => {:ok, -1}

In order to cope with Unicode character it is necessary to specify the binary option:

NodeJS.call("echo", ["’"], binary: true) # => {:ok, "’"}

There Are Rules & Limitations (Unfortunately)

• Function arguments must be serializable to JSON.
• Return values must be serializable to JSON. (Objects with circular references will definitely fail.)
• Modules must be requested relative to the path that was given to the Supervisor. E.g., for a path of /node_app_root and a file /node_app_root/foo/index.js your module request should be for "foo/index.js" or "foo/index" or "foo".

Running the tests

Since the test suite requires npm dependencies before you can run the tests you will first need to run

cd test/js && npm install && cd ../..

After that you should be able to run

mix test

Handling Callbacks and Promises

You can see examples of using promises in the tests here:

https://github.com/revelrylabs/elixir-nodejs/blob/master/test/nodejs_test.exs#L125

and from the JavaScript code here:

module.exports = async function echo(x, delay = 1000) {
  return new Promise((resolve) => setTimeout(() => resolve(x), delay))
}

https://github.com/revelrylabs/elixir-nodejs/blob/master/test/js/slow-async-echo.js