Applesoft BASIC in JavaScript
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jsbasic - Applesoft BASIC in JavaScript

This is hosted for playing with at http://inexorabletash.github.io/jsbasic/

Use git clone --recursive to get polyfill for older browsers.

Notes & Known Issues

  • The BASIC program is compiled to JavaScript before execution. Syntax errors are therefore detected at compile-time rather than at run-time as on a traditional interpreter. For example, the following program would run without errors on an Apple since the erroneous second statement is never reached. 10 END : CHR$(PRINT)
  • Handling of BASIC code that does not match the canonical LIST output format may not behave as on an Apple:
    • Keyword parsing differs from Applesoft command line. For example FOR I = S TO P doesn't collapse into FOR I = STOP.
  • Limitations:
    • Floating point overflow is only detected on variable assignment.
    • Only a subset of DOS 3.3 and ProDOS useful for basic file I/O are implemented.
    • Only a small number of common PEEK, POKE and CALL locations are supported.
    • Commands that refer to assembly routines (&, USR() etc.), shape tables, and tape I/O are not implemented.
  • Commands that operate on the program itself (LIST, RUN, DEL, etc.) are not implemented.
  • A handful of extensions are made beyond Applesoft BASIC:
    • To improve readability, lines may start with : and continue the previously numbered line.
    • DEF FN can define string functions
    • == can be used as =
    • CHR$() values > 255 do interesting things
    • HSCRN(x, y) allows probing the hi-res screen
    • hexadecimal literals e.g. $C010 can be used as numbers

You can run your basic programs from the command line (with only basic text input and output, and no graphics or DOS commands):

  • Clone the repository locally
  • On Windows, run from a command prompt via: cscript.exe cbasic.js your_program.txt
  • On Mac/Linux, install Mozilla Rhino, run from the command prompt via: java -jar PATH_TO/js.jar cbasic.js your_program.txt