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js-dos

js-dos runs DOSBox-X in the browser for Windows 3.x (win3x) and Windows 9x (win9x) titles. MS-DOS games continue to use the EmulatorJS dosbox-pure core.

Bundled in the full image, fetched from a CDN in slim

The full container image ships the js-dos runtime locally. The slim image has no local copy, so the player falls back to jsDelivr at runtime and needs outbound internet access from the browser (see Image Variants).

js-dos requires HTTPS

DOSBox-X uses the SharedArrayBuffer API, which browsers only expose in secure, cross-origin-isolated contexts, so RomM must be served over https:// for these games to run. Use a reverse proxy with TLS if you're still on plain HTTP.

Server owners can turn the player off with DISABLE_JSDOS=true (see Environment Variables).

Bundling a game

RomM passes the selected file directly to js-dos, so upload a ready-to-run js-dos bundle, not a regular zip of loose game files. The bundle is a zip archive carrying a .jsdos/dosbox.conf, and RomM only offers the player for files with a .jsdos extension, so rename the archive before uploading:

game.jsdos
    .jsdos/
        dosbox.conf
    WINDOWS/
    ...game files

The file extension must be .jsdos

A bundle left as game.zip scans in fine but never gets a Play button, because RomM gates the js-dos player on the file extension.

The configuration controls how the bundle boots. For example, a Windows 3.x bundle with Windows installed in the bundle root can use:

[dosbox]
machine=svga_s3
memsize=32

[autoexec]
@echo off
mount c .
c:
WIN GAMEDIR\GAME
  • mount c . mounts the bundle root as C:. js-dos does not add this mount automatically.
  • WIN GAMEDIR\GAME boots Windows straight into the game instead of Program Manager.

Windows 9x and disk-image layouts need different DOSBox-X configuration. Use the js-dos bundle cookbook or js-dos Game Studio, its browser-based bundle builder. Upload the result under the win3x or win9x platform. RomM uses js-dos only for those platforms and leaves dos with EmulatorJS.

Saves

js-dos stores filesystem changes in the browser, isolated by RomM user and game. They are not uploaded or synced with RomM. Quitting the player writes a final save, so wait for it to finish rather than closing the tab mid-game.

Saving depends on the application

Some applications save only when you exit back to Windows. Exit the application before quitting the player.