docs: add js-dos player for Windows 3.x / 9x

docs/Navigation.md

@@ -49,6 +49,7 @@ search:
     - [Uploads](using/uploads.md)
     - In-Browser Play
         - [EmulatorJS](using/in-browser-play/emulatorjs.md)
+        - [js-dos](using/in-browser-play/js-dos.md)
         - [MS-DOS](using/in-browser-play/ms-dos.md)
         - [Ruffle](using/in-browser-play/ruffle.md)
     - [Emulator Streaming](using/emulator-streaming.md)

docs/using/in-browser-play/js-dos.md

@@ -0,0 +1,69 @@
+---
+title: js-dos
+description: Play Windows 3.x and 9x games in the browser via DOSBox-X
+---
+
+<!-- trunk-ignore-all(markdownlint/MD033) -->
+
+# js-dos
+
+[js-dos](https://js-dos.com/) runs DOSBox-X in the browser and plays Windows 3.x (`win3x`) and 9x (`win9x`) titles that [EmulatorJS](emulatorjs.md) blank-screens. Native `dosbox-pure` (for example RetroArch) runs the same titles, so one bundle can carry both conventions.
+
+## Bundling a game
+
+Since the titles can be played in `dosbox-pure`, it is advisable to have the same title in `.zip` format bundling both `js-dos` and `dosbox-pure` conventions:
+- `js-dos` reads a [js-dos bundle](https://js-dos.com/jsdos-bundle.html): a zip whose `.jsdos/dosbox.conf` holds an `[autoexec]` that mounts the drive and launches Windows. **js-dos does not auto-mount**.
+
+<details>
+<summary>.jsdos/dosbox.conf</summary>
+
+```ini
+[dosbox]
+machine=svga_s3
+memsize=32
+
+[autoexec]
+echo off
+mount c .
+c:
+WIN GAMEDIR\GAME
+```
+
+</details>
+
+- `mount c .` is required because js-dos will not mount for you.
+- `WIN GAMEDIR\GAME` boots Windows straight into the game instead of Program Manager.
+- CD titles: add `imgmount d GAME.iso -t iso`, or extract the ISO to a folder and `mount d CDFOLDER -t cdrom -label GAMECD` if a title rejects `imgmount`.
+
+- `dosbox-pure` reads a root `DOSBOX.conf` (or `game.bat` and `setup.bat` for titles a bundled conf destabilizes). Its `[autoexec]` is the same minus `mount c .`, because `dosbox-pure` auto-mounts as `C:`.
+
+```text
+game.zip
+    .jsdos/
+        dosbox.conf
+    DOSBOX.conf
+    WINDOWS/
+    ...game files
+```
+
+Each engine reads its own config and ignores the other. js-dos is only needed in the browser, where EmulatorJS blank-screens these titles. Native `dosbox-pure` runs the same bundle.
+
+Upload the `.zip` under `win3x` or `win9x`. js-dos loads any zip containing `.jsdos/dosbox.conf`, so the same file also runs in native `dosbox-pure`. If you only need js-dos, omit the `dosbox-pure` config.
+
+## Saves
+
+js-dos auto-persists the emulated disk to your browser, so progress survives a reload. Saves are per-browser and per-game.
+
+<!-- prettier-ignore -->
+!!! info "Some apps only save on exit to Windows"
+    A few titles such as Fine Artist only save when you exit the app back to Program Manager. Exit to Windows before quitting.
+
+## Limitations
+
+- RomM-synced saves are not enabled yet. This is intentional for now.
+
+## Disabling the player
+
+Set `DISABLE_JSDOS=true`, the same as `DISABLE_EMULATOR_JS` and `DISABLE_RUFFLE_RS` for the other players.
+
+More in [In-Browser Play Troubleshooting](../../troubleshooting/in-browser-play.md).

docs/using/in-browser-play/ms-dos.md

@@ -9,6 +9,10 @@ description: Run DOS games in the browser via dosbox-pure
 
 DOS games run via the `dosbox-pure` core (part of [EmulatorJS](emulatorjs.md)). Create a DOS platform (folder named `dos`) and drop your games in. Operator tuning lives in [Configuration File → `emulatorjs`](../../reference/configuration-file.md#emulatorjs) (notably `disable_batch_bootup` for DOS-specific issues).
 
+<!-- prettier-ignore -->
+!!! info "Windows 3.x and 9x games use js-dos"
+    `dosbox-pure` runs DOS programs but cannot render Windows. Windows 3.x and 9x titles play through the [js-dos player](js-dos.md) under the `win3x` and `win9x` platform folders instead.
+
 <!-- prettier-ignore -->
 !!! tip "Upload games as `.zip`"
     `dosbox-pure` knows how to unzip and auto-mount zipped DOS games, which is much easier than packaging a raw folder.