A NES Emulator made in JavaScript for educational purposes. Try it!
Its 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.
Created by [r]labs.
⚠️ This is not a cycle-accurate emulator and performance is not the main concern.
npm install --save nes-emu
// configure video and audio:
const onFrame = (frameBuffer) => {
// write `frameBuffer` (a 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.
| 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. |
You can inspect the emulator state by using the global window.debug object.
Also, if you add ?debug to the URL and use a gamepad, shoulder buttons will behave as follows:
2--4
1--3
1: Enter debug mode
2: Exit debug mode
3: Hold to run frame
4: Hold to run scanline
FAQs
A NES emulator
We found that nes-emu demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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