Nōdo – call Node.js from Ruby

Nodo provides a Ruby environment to interact with JavaScript running inside a Node process.

ノード means "node" in Japanese.

Why Nodo?

Nodo will dispatch all JS function calls to a single long-running Node process.

JavaScript code is run in a namespaced environment, where you can access your initialized JS objects during sequential function calls without having to re-initialize them.

IPC is done via unix sockets, greatly improving performance over classic process/eval solutions.

Installation

In your Gemfile:

gem 'nodo'

Node.js

Nodo requires a working installation of Node.js.

If the executable is located in your PATH, no configuration is required. Otherwise, the path to to binary can be set using:

Nodo.binary = '/usr/local/bin/node'

Usage

In Nodo, you define JS functions as you would define Ruby methods:

class Foo < Nodo::Core

  function :say_hi, <<~JS
    (name) => {
      return `Hello ${name}!`;
    }
  JS

end

foo = Foo.new
foo.say_hi('Nodo')
=> "Hello Nodo!"

JS code can also be supplied using the code: keyword argument:

function :hello, code: "() => 'world'"

Async functions

Nodo supports calling async functions from Ruby. The Ruby call will happen synchronously, i.e. it will block until the JS function resolves:

class SyncFoo < Nodo::Core
  function :do_something, <<~JS
    async () => { return await asyncFunc(); }
  JS
end

Using npm modules

Install your modules to node_modules:

$ yarn add uuid

requireing your dependencies will make the library available as a const with the same name:

class Bar < Nodo::Core
  require :uuid

  function :v4, <<~JS
    () => {
      return uuid.v4();
    }
  JS
end

bar = Bar.new
bar.v4 => "b305f5c4-db9a-4504-b0c3-4e097a5ec8b9"

Aliasing requires

If the library name cannot be used as name of the constant, the const name can be given using hash syntax:

class FooBar < Nodo::Core
  require commonjs: '@rollup/plugin-commonjs'
end

Dynamic ESM imports

ES modules can be imported dynamically using nodo.import():

class DynamicFoo < Nodo::Core
  function :v4, <<~JS
    async () => {
      const uuid = await nodo.import('uuid');
      return await uuid.v4()
    }
  JS
end

Note that the availability of dynamic imports depends on your Node version.

Defining JS constants

class BarFoo < Nodo::Core
  const :HELLO, "World"
end

Execute some custom JS during initialization

class BarFoo < Nodo::Core

  script <<~JS
    // custom JS to be executed during initialization
    // things defined here can later be used inside functions
    const bigThing = someLib.init();
  JS
end

With the above syntax, the script code will be generated during class definition time. In order to have the code generated when the first instance is created, the code can be defined inside a block:

class Foo < Nodo::Core
  script do
    <<~JS
      var definitionTime = #{Time.now.to_json};
    JS
  end
end

Note that the script will still be executed only once, when the first instance of class is created.

Inheritance

Subclasses will inherit functions, constants, dependencies and scripts from their superclasses, while only functions can be overwritten.

class Foo < Nodo::Core
  function :foo, "() => 'superclass'"
end

class SubFoo < Foo
  function :bar, "() => { return 'calling' + foo() }"
end

class SubSubFoo < SubFoo
  function :foo, "() => 'subsubclass'"
end

Foo.new.foo => "superclass"
SubFoo.new.bar => "callingsuperclass"
SubSubFoo.new.bar => "callingsubsubclass"

Deferred function definition

By default, the function code string literal is created when the class is defined. Therefore any string interpolation inside the code will take place at definition time.

In order to defer the code generation until the first object instantiation, the function code can be given inside a block:

class Deferred < Nodo::Core
  function :now, <<~JS
    () => { return #{Time.now.to_json}; }
  JS

  function :later do
    <<~JS
      () => { return #{Time.now.to_json}; }
    JS
  end
end

instance = Deferred.new
sleep 5
instance.now => "2021-10-28 20:30:00 +0200"
instance.later => "2021-10-28 20:30:05 +0200"

The block will be invoked when the first instance is created. As with deferred scripts, it will only be invoked once.

Limiting function execution time

The default timeout for a single JS function call is 60 seconds and can be set globally:

Nodo.timeout = 5

If the execution of a single function call exceeds the timeout, Nodo::TimeoutError is raised.

The timeout can also be set on a per-function basis:

class Foo < Nodo::Core
  function :sleep, timeout: 1, code: <<~'JS'
    async (sec) => await new Promise(resolve => setTimeout(resolve, sec * 1000))
  JS
end

Foo.new.sleep(2)
=>  Nodo::TimeoutError raised

Setting NODE_PATH

By default, ./node_modules is used as the NODE_PATH.

To set a custom path:

Nodo.modules_root = 'path/to/node_modules'

Also see: Clean your Rails root

Logging

By default, JS errors will be logged to STDOUT.

To set a custom logger:

Nodo.logger = Logger.new('nodo.log')

In Rails applications, Rails.logger will automatically be set.

Debugging

To get verbose debug output, set

Nodo.debug = true

before instantiating any worker instances. The debug mode will be active during the current process run.

To print a debug message from JS code:

nodo.debug("Debug message");

Evaluation

While Nodo is mainly function-based, it is possible to evaluate JS code in the context of the defined object.

foo = Foo.new.evaluate("3 + 5")
=> 8

Evaluated code can access functions, required dependencies and constants:

class Foo < Nodo::Core
  const :BAR, 'bar'
  require :uuid
  function :hello, code: '() => "world"'
end

foo = Foo.new

foo.evaluate('BAR')
=> "bar"

foo.evaluate('uuid.v4()')
=> "f258bef3-0d6f-4566-ad39-d8dec973ef6b"

foo.evaluate('hello()')
=> "world"

Variables defined by evaluation are local to the current instance:

one = Foo.new
one.evaluate('a = 1')
two = Foo.new
two.evaluate('a = 2')
one.evaluate('a') => 1
two.evaluate('a') => 2

⚠️ Evaluation comes with the usual caveats:

• Avoid modifying any of your predefined identifiers. Remember that in JS, as in Ruby, constants are not necessarily constant.
• Never evaluate any code which includes un-checked user data. The Node.js process has full read/write access to your filesystem! 💥

Clean your Rails root

For Rails applications, Nodo enables you to move node_modules, package.json and yarn.lock into your application's vendor folder by setting the NODE_PATH in an initializer:

# config/initializers/nodo.rb
Nodo.modules_root = Rails.root.join('vendor', 'node_modules')

The rationale for this is NPM modules being external vendor dependencies, which should not clutter the application root directory.

With this new default, all yarn operations should be done after cding to vendor.

This repo provides an adapted version of the yarn:install rake task which will automatically take care of the vendored module location.

Working with web mocking frameworks like WebMock

Nodo uses HTTP via UNIX sockets to connect to its Node process. This may lead to conflicts during tests when using WebMock or other tools which interfere with Net::HTTP. In order to work with WebMock, you need to enable its allow_localhost option:

WebMock.disable_net_connect!(allow_localhost: true)