Nes-emu NPM | npm.io

NesCore

A NES Emulator made in JavaScript for educational purposes. Try it!

It's main objective is to reflect the NES internals as simply as possible by using clean, object-oriented code. It doesn't have any complex bitwise operations, huge switch-case statements or files with lots of magic numbers.

⚠️ This is not a cycle-accurate emulator and performance is not the main concern ⚠️

Features

👾 It emulates the NES
👨‍🔧 It plays Super Mario Bros. 3!
💻 CPU
- All official instructions are implemented
- nestest passes ✔️
Fully functional 🖥️ PPU and 🔊 APU
🔌 Supported mappers
- Mapper 0: NROM
- Mapper 1: MMC1
- Mapper 2: UxROM
- Mapper 3: CNROM
- Mapper 4: MMC3
🐏 SRAM support
💾 Save states support
🌎 Web frontend using Web Workers and Gamepad API

Usage

npm install --save nes-emu

// configure video and audio:
const onFrame = (frameBuffer) => {
  // write `frameBuffer` (an Uint32Array) to screen...
};
const onSample = (sample) => {
  // write `sample` (a number) to audio buffer...
};

// create an instance:
const nes = new NES(onFrame, onSample);

// load a game:
nes.load(rom); // rom = Uint8Array

// run at 60 fps, or as fast as you can:
{
  nes.setButton(1, "BUTTON_A", true); // player = 1, button = A, pressed = true
  nes.setButton(2, "BUTTON_DOWN", false); // player = 2, button = DOWN, pressed = false
  // ...set the rest of the buttons
  nes.frame();
}

// save / restore states:
const saveState = nes.getSaveState();
nes.setSaveState(saveState);

👀 Have a look at the demo implementation for more details. When running the demo (npm start) you can add ?debug to the URL to enable a global window.debug object.

Full API

Method	Parameters	Description
constructor	`onFrame`, `onSample`, `logger`	Creates an emulator's instance. All properties can be set at any time.
`load`	`rom`, `saveFileBytes`	Loads a ROM. If a `saveFileBytes` array is provided, it sets the SRAM content.
`frame`		Runs the emulation for a whole video frame.
`samples`	`requestedSamples`	Runs the emulation until the audio system generates `requestedSamples`.
`scanline`		Runs the emulation until the next scanline.
`setButton`	`player`, `button`, `isPressed`	Sets the `button` state of `player` to `isPressed`. The `button` can be one of: `["BUTTON_A", "BUTTON_B", "BUTTON_SELECT", "BUTTON_START", "BUTTON_UP", "BUTTON_DOWN", "BUTTON_LEFT", "BUTTON_RIGHT"]`
`clearButtons`	`player`	Sets all buttons of `player` to a non-pressed state.
`getSaveFile`		Returns an array with the SRAM bytes, or null.
`getSaveState`		Returns an object with a snapshot of the current state.
`setSaveState`	`saveState`	Restores a `saveState`.