Basic Support for MASM/TASM v2.x

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Basic language support for assembly in DOS environment. It may be suitable for studying MASM/TASM in DOSBox or courses like Principles and Peripheral Technology of Microprocessor.

• Language Support: Offers grammar validation, basic outline view, hover tips, and code formatting support for DOS assembly language
• Status Bar: Quick access to switch DOS emulator and assembler independently, with executable paths shown
• Run and Debug: Right-click on the VS Code editor panel to run and debug your code
• Diagnose: Processes the output of ASM tools and displays diagnostics in VS Code
• Supports all platforms including Web support try me in your browser by click vscode.dev.
• Note: This extension is built for learning assembly in DOS, and it does not work with Win32 assembly

Demo

Demo 1: Language Features

Format Code	Diagnose

The extension provides language features such as hover hints, code formatting, and jump to definition for the assembly language ID.

Code Formatting

The built-in formatter follows the style of sample .asm files:

• Labels at column 0, instructions indented with tabs
• Top-level directives (.386, .model, .STACK, include, etc.) stay at column 0
• Blank lines preserved as truly empty
• Original operand spacing and comments preserved
• Formatting is idempotent — running it twice produces the same result
• Use the Format Document command (Shift+Alt+F) to apply formatting. You can also use other assembly language support extensions (e.g., the asm-collection language ID) by installing ASM Code Lens.

Demo 2: Run and Debug

Using TASM via DOSBox	Using MASM via jsdos

When editing assembly files, right-click in the editor panel to access the following options:

1. Open Emulator: Launch DOSBox and prepare the runtime environment
2. Run ASM Code: Assemble, link, and execute the program
3. Debug ASM Code: Assemble, link, and debug the program

Run/Debug Notes

• The extension copies your file to an isolated directory before assembling, to keep your workspace clean.
• Note that this extension is not optimized for complex projects.

Project Configuration with dosasm.jsonc

For multi-file projects or custom build workflows, you can place a dosasm.jsonc file in your project directory. When you right-click an .asm file to run/debug, the extension searches upward from the file's directory for dosasm.jsonc. If found, it uses the configuration defined there instead of the default settings.

Example dosasm.jsonc (see dosasm.jsonc v1):

• multi file project sample
• compile to .com file
• Turbo C example

Template variables:

• ${file} — the full path of the assembly file in DOS
• ${filename} — the file path without extension
• ${actionFolder} — the directory containing the dosasm.jsonc file
• ${<built-in>/TASM.jsdos} — the extracted bundle folder path (the extension automatically extracts the .jsdos zip bundle and mounts the resulting folder)

How it works:

• The action.before commands set up the DOS environment (mount drives, set PATH, etc.)
• The action.run commands assemble, link, and execute the program
• The action.debug commands assemble, link, and launch the debugger
• The action.open commands are used when opening the emulator without running
• When dosasm.jsonc is found, the default single-file mount behavior is skipped — the before section fully controls the environment setup

Copy file before run/debug:

• action.copyFileAs (string | null): Controls whether the active file is copied before run/debug
  • String: file is copied to this path (relative to the action folder)
  • null: file is not copied, the original file path is used directly
• Bundle extraction: ${<built-in>/TASM.jsdos} references a built-in .jsdos zip bundle. The extension extracts this bundle to a folder and replaces the variable with the folder path, so you can mount it as a DOS drive

Platform Support

This extension interfaces with the DOSBox(-X) binary via Node.js's child_process module. You must install DOSBox or DOSBox-X first to use this feature.

Since VS Code is primarily built with JavaScript (TypeScript), we support the WebAssembly (Wasm) version of DOSBox(-X) — namely js-dos. The extension bundles all required js-dos files, and it uses js-dos as the default DOS emulator for Web platform support.

Docs & Acknowledgments & Licenses

• Special thanks to my teacher, Mr. Han. Wishing 2020 and the coming 2021 to be happy and fulfilling years.
• Inspired by Woodykaixa's masm-code project
• Thanks to the excellent DOS emulators: DOSBox-x, DOSBox, caiiiycuk's js-dos, and msdos-player
• Thanks to Roncho's extension Assembly (TASM) and blindtiger's masm for reference on assembly language support
• We welcome issues and pull requests to help improve this extension
• Acknowledgments
• Additional Information: Wiki

Enjoy! 😊