JSNES

NES emulator for the browser (JavaScript + Vite).

Live Demo: https://jsnes.dev/

Current Features

• Load local .nes ROM files from a folder picker.
• Mapper support: NROM (000), MMC1 (001), UNROM (002), CNROM (003).
• Quick Save / Quick Load with slot selector (SLOT 0-9).
• Quick states are persisted in IndexedDB per ROM + slot.
• Battery SRAM (in-game save data) auto-save/auto-load via IndexedDB.
• Battery save export/import as .sav files.

Save System

Two save systems are available and they are independent:

1. Quick State

• Buttons: Q-SAVE, Q-LOAD
• Scope: full emulator runtime state
• Storage: IndexedDB (per ROM + selected quick slot)

2. Battery Save (SRAM)

• Scope: in-game save data (for games that use SRAM)
• Storage: auto-managed IndexedDB entry (dedicated internal battery slot)
• File IO: BATT EXPORT, BATT IMPORT for .sav

Usage

1. Open the app.
2. Click LOAD ROM FOLDER.
3. Select a local directory containing .nes files.
4. Click a ROM in the list to start.
5. Use RESET to restart the currently running game.

Controls

NES	Keyboard
Move	Arrow keys
A Button	Z
B Button	X
Start	Enter
Select	Space
Emulator Quit (debug)	Q
Emulator Reset (hotkey)	R

Development

Install dependencies:

npm install

Run dev server:

npm run dev

Build:

npm run build

Preview production build:

npm run preview

Notes

• Folder loading uses the File System Access API (showDirectoryPicker), which is best supported in Chromium-based browsers.
• Save data is origin-scoped. Clearing browser site data removes IndexedDB saves.

Tested Games

NROM (iNES Mapper 000)

MMC1 (iNES Mapper 001)

UNROM (iNES Mapper 002)

CNROM (iNES Mapper 003)

References

• https://www.nesdev.org/wiki/Nesdev_Wiki
• https://www.nesdev.org/wiki/NES_reference_guide

License

MIT. See LICENSE.