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Applesoft BASIC in JavaScript
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README.md

jsbasic - Applesoft BASIC in JavaScript

This is hosted for playing with at http://calormen.com/applesoft/

For older browsers, the code depends on various polyfills. For syntax highlighting, the editor optionally uses CodeMirror and custom BASIC parser/styles. Clone these into sibling directories, so you end up with a structure like:

jsbasic/
polyfill/
CodeMirror/

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.
  • 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
  • To improve readability, lines may start with : and continue the previously numbered line.
  • Floating point overflow is only detected on variable assignment.
  • The DOS operating system implements only a subset of DOS 3.3 and ProDOS useful for basic file I/O.
  • Except for a small number of compatibility shims for common operations (e.g. keyboard strobe), commands that refer to assembly routines (PEEK, POKE, 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 implemented.

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

  • On Windows, download basic.js and run from a command prompt via: cscript.exe basic.js your_basic_program.txt
  • On Mac/Linux, install Mozilla Rhino, download basic.js and run from the command prompt via: java -jar PATH_TO/js.jar basic.js your_program.txt

To Do

  • Snapshot and/or link sensibly to the polyfills
  • Implement DOS functionality for consoles

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