opal gem

Uses Ruby gems in Opal:

• No C/FFI gems.
• Gems uses Opal's unsupported features, e.g.
  • String mutability
  • difference between String and Symbol
  • Filesystem, treads, shells

You can stub some missed features:

Opal::Processor.stub_file('fileutils')

And hide codes at compile time:

unless RUBY_ENGINE == 'opal'
  Code unportable to Opal here.
end