Applesoft BASIC Interpreter in Javascript

By Joshua Bell | Applesoft BASIC Quick Reference | Notes | Known Issues | To Do | Links | History

Welcome Slashdot! Be sure to check out my other Apple II retrocomputing project: vnIIc

Enter code below       Select a file... DEMOS TRADER SIMPLE.PONG HACKER LOGO (markwstock) RANDOM LORES (John Melesky) RANDOM HIRES (John Melesky) PRIME SIEVE (Kevin Miller) SIERPINSKI TRIANGLES (Kevin Miller) STRING ART (Chris Heric) Show Input Devices

Notes

• It can be run from the command line on Windows. Download basic.js and run as: cscript basic.js myprogram.txt

Known Issues

• Handling of source 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 COLOR = is not parsed as the COLOR= keyword; FOR I = S TO P doesn't collapse into FOR I = STOP
  • The interpreter doesn't actually care about line numbers for statement ordering (just for GOTO/GOSUB targets and IF statements). So 20 PRINT "A", 10 PRINT "B" will just print A, then B
• Text display is 80 columns. Lores display is 40 columns (single-lores, not double-lores as found on the //c+)
• Commands that refer to assembly routines (CALL, USR etc.), shape tables, or tape I/O are not implemented.
• Commands that operate on the program itself (LIST, RUN, DEL, etc.) are not yet implemented.
• Only primary graphics pages are supported (no HGR2)

To Do

• Pri 1: Treat correctly handele line numbers

Links

• 6502asm.com - a 6502 assembler/emulator in JavaScript
• Quite BASIC - a similar project aimed at teaching programming
• NG-BASIC for Javascript Navaho Gunleg's interpreter
• BASIC Programming Resources

History

2008-05-01:

Fixed NEXT I,J,... to terminate multiple loops - thanks to Scott Alfter for pointing this out

Bowing to popular demand, it now supports ? as an alias for PRINT

2008-03-15:

Implemented ONERR GOTO line and RESUME, including POKE 216,0

Added demo for ONERR, added ONERR support to sequential file access demo

Fix hires graphics on Safari - not sure when it broke

2008-03-14:

Code cleanup c/o jslint.com

Bug fix: INPUT A,B,C no longer worked. Probably mis-re-factored at some point.

2007-12-08:

Implement file writing (to client-side VFS only), including APPEND operations

Added DOS DELETE command

GR does implicit HTAB 1 : VTAB 24

PEEK(49168) has the same effect as POKE 49168,N

As a convenience, PEEK and POKE at 49200/-16336 (speaker toggle) now accepted, but a no-op

As a convenience, spaces now accepted before = forCOLOR= and HCOLOR=

2007-11-22:

Added button to submit your sample (via email) for inclusion

Added SIMPLE.PONG sample c/o USENET post by mad.scientist.jr

Improved comment handling (doesn't tokenize)

2007-10-22:

Make GET support keyboard flag, so IF PEEK(-16384) > 127 THEN GET A$ works

2007-10-20:

Bug fix: User could type after hitting Stop. Now TTY state is reset.

Added missing statement: ON expr GOSUB ...

RND(0) returns last, negative reseeds

2007-10-14:

Fixed location of paddle button 3 (C060)

2007-09-22:

Implemented scaling in ExplorerCanvas (source); hires now scaled somewhat correctly in IE

Bug fixes: HOME would force full-screen text; HPLOT can now plot a single pixel

2007-09-20:

Added hires support via canvas tag

Display switches (POKE 49232...49239, not counting page 2) supported.

Added text window support: POKE 32,left : POKE 33,width : POKE 34,top : POKE 35,bottom

2007-09-16:

Added full screen lores support via POKE 29234,0

Fixed keyboard input on Safari - hacky, but logical

2007-09-15:

Added Mandelbrot set demo to DEMOS

Added PEEK and POKE shims

Added paddle buttons: Home = 0 = Open Apple, End = 1 = Solid Apple, Page Up = 2, Page Down = 3

Added Caps Lock (defaults to on; real Caps Lock key toggles it; this means it usually ends up in an inverted state)

Round numerical results to 8 decimal places (hacky)

2007-09-10:

Added demo file links, cleaned up UI a bit.

Added hacky PR#0/PR#3 support (to set 40 columns)

2007-09-09:

Execute multiple steps before yielding. Increases perceived performance by about 10x.

Adjust lores colors per Linards Ticmanis on comp.sys.apple2.

Added Joystick, reorganized web pages

2007-09-04:

Added MON/NOMON support.

Fixed bugs with: READ into arrays, two argument MID$, e-format number parsing, DOS null command

2007-09-03:

Bugfixes: SPC() and TAB() followed by ; in PRINT statements. DOS parameter lists can include spaces.

2007-09-02:

Oops - FRE is a function not a statement. Fixed!

2007-09-01:

Implemented DATA/READ/RESTORE

2007-08-31:

Implemented DEF FN

2007-08-30:

Implemented DIM. File reads complete.

2007-08-27:

Added preliminary DOS implementation. Sequential access read only; there's a file called "JABBERWOCKY" to try.

2007-08-24:

Fixed bugs with string variables, key presses in IE, and HTML tweaks for better layout and lo-res sizing

2007-06-05:

Added paddle support (PDL)

2007-06-03:

Added lores graphics support (GR, PLOT, HLIN, VLIN, COLOR=, SCRN)

2007-05-01:

Extracted step mechanism from interpreter, so web page can introduce delays; no longer case-sensitive to keywords

2007-04-29:

Fixed command-line mode again

2007-04-27:

Added screen emulation (e.g. HOME, HTAB, VTAB) and input (e.g. GET)

2007-04-24:

Integrated into browser (display and event model)

2007-04-21:

Project started; interpreter functional via WSH on Windows