Skookum JS is build by abstracting the undelying platform as little as possible and giving the developer full control of low level POSIX APIs.

The VM is modeled after other runtimes such as Ruby’s or Python’s.

The runtime can be logically divided into 3 parts:

  • The interpreter CLI: it’s a relatively simple application which creates a sjs VM and evaluates code using it. For the REPL (interactive mode) it uses linenoise.
  • The VM library: sjs (the CLI) links with libsjs (the VM), which encapsulates all functionality and embed the Duktape engine. This makes other applications capable of running JavaScript code by linking with libsjs and creating a VM.
  • The modules: in sjs modules can be either written in pure JavaScript or in C. See the Modules section.

The VM

The sjs VM is currently single threaded, bu thread aware. That is: users can create as many VMs as they wish, as long as there is a single VM running for a given thread. There is no global state. There is no builtin mechanism for inter-VM communication.

See the Embedding sjs in your application section for details on the C API.


Skookum JS was not inspired by browser JavaScript runtimes but by more “traditional” runtimes such as Ruby’s MRI or Python’s CPython.

This means that the model is not inherently asynchronous and event-driven, as in a browser or Node JS. sjs does provide the necessary tools to build asynchronous / event-driven frameworks on top of the provided modules.