Recently I have spent some time doing experiments with Opal rb 1.0, to use Ruby in place of Javascript.
Here are some tests that could be useful.

Require other sources

There are 3 methods to include other sources: require, require_relative and require_tree. Also autoload can be used to include.
Let’s see an example with require:

# foo.rb
puts 'foo'
# bar.rb
require './foo.rb'
puts 'bar'

Run it with: opal bar.rb
And the output is:

foo
bar

Using a NodeJS component

Here are some points to use a JS library in an Opal project, for example colors.
To create a new project and add the library:

yarn init
# Enter the required fields
yarn add colors

Require a module, assign the reference and call a method:

require 'native'
Colors = Native(`require('colors/safe')`)
puts Colors.green('bar')

Execute a JS method on a Ruby string:

`require('colors')`
puts 'foo'.JS[:red]

Compile and run the code:

opal -c app.rb > app.js
node app.js

JS export

Export variables:

`exports.test1 = 'A string'`
# or
`exports`.JS[:test1] = 'Another string'
# or
Native(`exports`).test1 = 'Last string'

To access to the exported variable in another file:

puts `exports.test1`
# or
puts `exports`.JS[:test1]
# or
puts Native(`exports`).test1

Export methods:

`exports`.JS[:test1] = `function() { console.log("A method") }`
# or
`exports`.JS[:test1] = -> { puts 'Another method' }

To access to the exported method in another file:

`exports.test1()`
# or
`exports`.JS.test1
# or
Native(`exports`).test1