jsbasic - Applesoft BASIC in JavaScript

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

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