Engines

Narwhal is a standard library and tools for multiple JavaScript engines; each engine has its own library. Use tusk engine {name} to select an engine, or edit narwhal.conf. The following engines are presently in development:

• rhino: is the default and most complete engine, based on Mozilla Rhino for Java, used for out-of-the-box functionality.
• k7: is a v8 based engine, in development by Sébastien Pierre.
• helma: is based on Rhino with extensions, being developed by Hannes Wallnöefer.
• xulrunner: is in development for Firefox extensions and XULRunner applications on the Spidermonkey engine by Irakli Gozalishvili, Christoph Dorn, and Zach Carter.
• jaxer: is an engine based on Mozilla SpiderMonkey, for deploying web pages with both server and client side scripts, being developed by Nathan L Smith.
• v8cgi: is based on the work of Ondrej Zara, and has not been updated in a long while.
• default: is a catchall engine that implements modules that can be shared among engines.
• browser: will eventually be available for client side loading of modules with various techniques.
• secure: will eventually be available for dependency injection sandboxed module systems within some other engines.

Creating new Engine Adapters

We have a template for new engines at engines/template that you can copy to engines/{name} and fill in the blanks. These consist of:

1. An executable (shell script or binary) at engines/{name}/bin/narwhal-{name} that executes the interpreter engine of choice and causes it to load a bootstrap script. This script will be loaded by bin/narwhal with the environment variable NARWHAL_HOME set to the Narwhal project directory and NARWHAL_ENGINE_HOME set to the engine directory. This script will be run if NARWHAL_ENGINE is set to your engine name. You can set NARWHAL_DEFAULT_ENGINE or NARWHAL_ENGINE in a narwhal.conf in your Narwhal project directory (template provided).

2. A “thunk”, at engines/{name}/bootstrap.js that evaluates narwhal.js and passes the returned function a preliminary system object with a few required properties (global, evalGlobal, engine, engines, print, evaluate, prefix, fs.read, and fs.isFile). This should be enough to get to an interactive console.

3. Engine implementations for core modules, such as file and system located in engines/{name}/lib/. You can implement file-engine instead of file if you implement the subset of the ServerJS file API used by lib/file.js (and similar for io, os, binary, etc). The next steps are:

   • system: You must implement system.args to be able to pass command line options to Narwhal.

   • file: To enable the package system you must implement list, canonical, mtime, isDirectory, isFile.