JSFunge-98 is an (almost) standards-compliant Befunge-98 interpreter written in pure JavaScript. Try it here!


  • befunge98.html: the main frontend page for the interpreter.
  • befunge98.css: the stylesheet for the interpreter.
  • befunge98.js: the interpreter control code.
  • befunge98-engine.js: the actual interpreter. This file contains everything needed for actually running the interpreter.


Browser interface

JSFunge-98 has a browser interface that allows for:

  • writing code
  • loading built-in examples
  • loading code files from the user's computer
  • pre-entering input or using an interactive console (todo)
  • running the code, with optional delay
  • stepping code instruction by instruction
  • debugging with stack and Funge-Space views (todo) and
  • entering command line arguments.


JSFunge-98 implements almost the entire Befunge-98 specification. Filesystem Funge is not implemented for obvious reasons. Concurrent Funge-98 support may come in the future.

The only unimplemented required feature is the shrinking of Funge-Space when areas are changed to spaces. Also, putting values to extremely large positions will cause memory problems, as the use of memory is not optimized for them.

JSFunge-98 has been tested against the Mycology test suite, and passes all tests except for the ones related to the shrinking of Funge-Space (and input, which is currently untestable).

The following fingerprints are currently implemented:

  • MODU
  • NULL
  • ROMA

Known issues

  • Input is not working yet.
  • The about button is nonfunctional for now.

Upcoming features

  • Live debugger, with stack and Funge-Space views.
  • Saving files.
  • Concurrent Funge-98.
  • Working input.