Ruby runtime and library on top of Javascript
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Opal is a ruby runtime for javascript and includes a ruby to javascript source-to-source compiler. The core libraries are written in ruby.

Homepage: Github:

See homepage for examples etc.


Ruby is under work towards version 0.4.0. To use the latest code, on this master branch, clone the repo:

$ git clone git://

The code is nearly ready to run. Firstly, however, you need to compile the corelib (written in ruby) into javascript, so run:

$ rake opal

Which will build the corelib into vm/. Opal is now ready to use.


Opal has a built in REPL that uses therubyracer to hold a built in context. Try the REPL with:

$ ruby -I ./lib bin/opal irb

This will use the local directory to run the virtual machine.

Running tests

To quickly run all tests:

$ rake test

Project structure

This repo contains the code for the opal gem as well as the opal core library and runtime. Files inside bin/ and lib/ are the files that are used as part of the gem and run directly on your ruby environment.

corelib/ contains opal's core library implementation and is not used directly by the gem. These files are precompiled during development ready to be used in the gem or in a browser.

runtime/ contains opal's runtime written in javascript. It is not used directly by the gem, but is built ready to use in the js contexts that opal runs.

stdlib/ contains the stdlib files that opal comes packaged with. The gem does use these, but only as required. Opal does not include the full opal stdlib, and some parts are actually written in javascript for optimal performance. These can be require() at runtime.

opal.js and opal-parser.js are included in the gem, but not the source repo. They are the latest built versions of opal and its parser which are built before the gem is published.