Skip to content

Web Interface Guide

The MBASIC Web IDE provides a full-featured BASIC programming environment accessible from any modern web browser.

Main Components

The Web UI has a vertical layout with these components:

Located at the top with File, Edit, Run, View, and Help menus. See Menu Functions below for details.

Toolbar

Quick-access buttons below the menu bar for common operations: - Run (▶️ green) - Start program execution - Stop (⏹️ red) - Stop running program - Step (⏭️) - Execute all statements on current line - Stmt (↻) - Execute one statement - Cont (▶️⏸️) - Continue execution after pause

Additional file operations are available through the File menu.

Program Editor (Top)

Write your BASIC program here.

  • Automatic line numbering when you press Enter (configurable via Settings)
  • Example: Type PRINT "HELLO" and press Enter → becomes 10 PRINT "HELLO"
  • Successive lines auto-increment: next line becomes 20, 30, 40, etc. (increment is configurable)
  • Manual numbering: You can still type your own line numbers if desired

Example workflow: 

Type: PRINT "Hello"
Press Enter → becomes: 10 PRINT "Hello"

Type: FOR I=1 TO 5
Press Enter → becomes: 20 FOR I=1 TO 5

Type: NEXT I
Press Enter → becomes: 30 NEXT I

Output (Middle)

See program output and error messages.

  • Shows results when you run your program
  • Displays error messages and diagnostics
  • Shows immediate command results

Command (Bottom)

Type immediate commands that execute without adding to your program.

  • No automatic line numbering - commands run immediately
  • Example: Type PRINT 2+2 → shows 4 without adding to program
  • Useful for testing expressions and quick calculations

Try these examples: 

Type: PRINT 2+2
Press Enter → Output shows: 4

Type: X=10: PRINT X*X
Press Enter → Output shows: 100

Type: FOR I=1 TO 3: PRINT I: NEXT I
Press Enter → Output shows: 1 2 3

When to use Command vs Editor: - Command - Quick calculations, testing expressions, checking variables - Editor - Writing programs you want to save and run multiple times

File Menu

  • New - Clear the editor and start a new program
  • Open - Open a .bas file from your computer (via browser file picker)
  • Save - Download current program to your computer as a .bas file
  • Save As - Download with a new filename
  • Clear Output - Clear the output area

Note: An "Open Example" feature to choose from sample BASIC programs is planned for a future release.

Edit Menu

  • Copy - Copy selected text to clipboard
  • Paste - Paste from clipboard ({{kbd:paste:web}})
  • Select All - Select all editor text
  • Sort Lines - Sort selected lines numerically by line number
  • Smart Insert - Insert lines intelligently between existing line numbers
  • Settings - Configure auto-numbering, case handling, and other interpreter options

Run Menu

  • Run Program - Parse and execute the current program
  • Stop - Stop a running program
  • Toggle Breakpoint - Set or remove a breakpoint at a specific line number
  • Clear All Breakpoints - Remove all breakpoints
  • Continue - Resume execution after a breakpoint or step
  • Step Line - Execute all statements on the current line, then pause
  • Step Statement - Execute one statement, then pause

View Menu

  • Show Variables - Open the Variables Window to view and monitor program variables in real-time

Help Menu

  • Help - Open this help browser

Writing Programs

  1. Type your BASIC program in the Program Editor (top area)
  2. Press Enter after each statement - line numbers are added automatically
  3. Click Run → Run Program to execute
  4. View output in the Output area (middle)

Auto-Numbering

The Program Editor automatically adds line numbers when you press Enter:

  • First line: Starts at 10 (configurable in Settings)
  • Subsequent lines: Increment by 10 (20, 30, 40...) - configurable in Settings
  • Manual numbering: You can still type your own line numbers if desired
  • Only in Editor: The Command area does NOT auto-number (it runs commands immediately)
  • Configurable: Use the Settings dialog (⚙️ icon) to change the increment or disable auto-numbering entirely

Example Program

10 PRINT "Hello from MBASIC!"
20 FOR I = 1 TO 5
30   PRINT "Count: "; I
40 NEXT I
50 END

File I/O

File operations in the web UI work with an in-memory filesystem:

  • Files are stored in server memory (sandboxed, per-session)
  • Each user/session has their own isolated filesystem
  • Files persist during your session (but are lost on page refresh or session end)
  • No access to the server's real filesystem (security)

Important: Programs and data created via BASIC file I/O commands (OPEN, PRINT #, etc.) exist only in memory during your browser session. To save your BASIC program source code permanently, use File → Save to download it to your computer.

File Limits

  • Maximum 20 files per user
  • Maximum 512KB per file

Example File I/O

10 REM Write to a file
20 OPEN "O", #1, "DATA.TXT"
30 PRINT #1, "Hello, file!"
40 CLOSE #1
50 REM Read from the file
60 OPEN "I", #1, "DATA.TXT"
70 INPUT #1, A$
80 PRINT "Read: "; A$
90 CLOSE #1

Language Features

The Web UI supports all MBASIC 5.21 language features, including:

Settings Commands

You can configure interpreter behavior using BASIC commands in your program or the Command area:

REM Configure case handling for variables
SET "variables.case_conflict" "error"

REM Configure keyword capitalization
SET "keywords.case_style" "force_capitalize"

REM View all current settings
SHOW SETTINGS

For complete details on case handling and other language settings, see the Case Handling Guide.

Security & Privacy

The web UI is designed for safe multi-user access:

  • ✅ Sandboxed - No access to server files
  • ✅ Isolated - Your files are private to your session
  • ✅ Limited - Resource limits prevent abuse
  • ✅ Session-based - Data cleared when session ends

Keyboard Shortcuts

  • {{kbd:paste:web}} - Paste into editor
  • {{kbd:select_all:web}} - Select all
  • {{kbd:copy:web}} - Copy selection

Browser Compatibility

Works best with modern browsers: - Chrome/Edge 90+ - Firefox 88+ - Safari 14+

Limitations

Compared to desktop UIs, the web UI: - Cannot directly access local filesystem (but can load files via browser file picker) - Limited debugger support (basic breakpoints only via Run menu) - Files don't persist after session ends (stored in server memory per-session)

Troubleshooting

Program Won't Run

  • Check for syntax errors in output
  • Ensure all lines have line numbers
  • Look for missing END statement

File I/O Errors

  • Check you haven't exceeded 20 file limit
  • Ensure files aren't too large (>512KB)
  • Remember to CLOSE files after use

Can't Paste Code

  • Use {{kbd:paste:web}} (not right-click menu in some browsers)
  • Try Edit → Paste from menu

About MBASIC 5.21

This is an implementation of MBASIC-80 version 5.21, originally released for CP/M systems in 1981. It provides compatibility with classic BASIC programs from that era.

For language documentation, see: - 📕 Language Help - BASIC language syntax and commands - 📗 MBASIC Help - MBASIC 5.21 specific features