Module System - Friday Night Funkin'

The Module system enables you to create persistent mods that receive events throughout the game’s lifecycle. Modules are scripted classes that can be active at all times or conditionally based on the current game state.

Overview

Modules are powerful because they:

Persist across states: Continue running when the player navigates between menus and gameplay
Receive all events: Can respond to any game event without needing specific context
Support priorities: Control the order in which modules receive events
Can be toggled: Activate/deactivate dynamically based on conditions
State-scoped: Optionally limit events to specific game states

Creating a Module

Modules are created as .hxc script files in your mod’s scripts directory.

Basic Module Structure

// scripts/MyModule.hxc
import funkin.modding.module.Module;

class MyModule extends Module {
  public function new() {
    super('my-module'); // Module ID
  }
  
  public override function onCreate(event:ScriptEvent):Void {
    trace('MyModule created!');
  }
  
  public override function onUpdate(event:UpdateScriptEvent):Void {
    // Called every frame
  }
}

Module Parameters

public function new(moduleId:String, priority:Int = 1000, ?params:ModuleParams)

moduleId
Unique identifier for your module. Use kebab-case by convention. priority (default: 1000)
Determines event processing order. Lower numbers = higher priority (processed first). params (optional)
Configuration object:

state: Limit module to only receive events when in this specific state

Example: State-Scoped Module

import funkin.modding.module.Module;
import funkin.play.PlayState;

class GameplayOnlyModule extends Module {
  public function new() {
    // Only active during gameplay
    super('gameplay-only', 1000, {state: PlayState});
  }
  
  public override function onBeatHit(event:SongTimeScriptEvent):Void {
    // This only fires during PlayState
    trace('Beat ${event.beat} hit!');
  }
}

Module Properties

Active State

public var active(default, set):Bool = true;

Controls whether the module receives events. Inactive modules are skipped.

class ToggleableModule extends Module {
  public function new() {
    super('toggleable');
    
    // Start inactive
    this.active = false;
  }
  
  public function activate():Void {
    this.active = true;
  }
  
  public function deactivate():Void {
    this.active = false;
  }
}

Priority

public var priority(default, set):Int = 1000;

Modules with lower priority numbers receive events first.

class HighPriorityModule extends Module {
  public function new() {
    super('high-priority', 1); // Receives events first
  }
}

class LowPriorityModule extends Module {
  public function new() {
    super('low-priority', 9999); // Receives events last
  }
}

State Association

public var state:Null<Class<Dynamic>> = null;

If set, the module only receives events when the game is in this state or substate.

Core Lifecycle Events

onCreate

public function onCreate(event:ScriptEvent):Void

Called when the module is first created, before the title screen appears.

public override function onCreate(event:ScriptEvent):Void {
  trace('Module initialized!');
  
  // Load configuration
  loadConfig();
  
  // Register custom assets
  registerAssets();
  
  // Set up global state
  initializeGlobalState();
}

It may not be safe to reference other modules in onCreate since they may not be loaded yet.

onDestroy

public function onDestroy(event:ScriptEvent):Void

Called when a module is destroyed. Currently only happens when reloading modules with F5.

public override function onDestroy(event:ScriptEvent):Void {
  // Clean up resources
  cleanupAssets();
  saveState();
  removeEventListeners();
}

onUpdate

public function onUpdate(event:UpdateScriptEvent):Void

Called every frame.

public override function onUpdate(event:UpdateScriptEvent):Void {
  // event.elapsed = delta time in seconds
  var dt = event.elapsed;
  
  // Update custom logic
  updateParticles(dt);
  checkInputs();
}

onScriptEvent

public function onScriptEvent(event:ScriptEvent):Void

Called for ANY script event. Use this as a catch-all or for custom events.

public override function onScriptEvent(event:ScriptEvent):Void {
  trace('Received event: ${event.type}');
  
  // Handle custom events
  if (event.type == 'my-custom-event') {
    handleCustomEvent(event);
  }
}

Gameplay Events

Modules implement IPlayStateScriptedClass and receive all gameplay events.

Note Events

public override function onNoteIncoming(event:NoteScriptEvent):Void {
  // Note is approaching the strumline
  var note = event.note;
  trace('Note incoming: direction=${note.direction}');
}

public override function onNoteHit(event:HitNoteScriptEvent):Void {
  // Note was hit by player or opponent
  var note = event.note;
  
  if (note.mustPress) {
    trace('Player hit note! Accuracy: ${event.accuracy}');
  } else {
    trace('Opponent hit note!');
  }
}

public override function onNoteMiss(event:NoteScriptEvent):Void {
  // Note was missed
  trace('Note missed!');
}

public override function onNoteGhostMiss(event:GhostMissNoteScriptEvent):Void {
  // Player pressed key with no note present
  trace('Ghost miss on direction: ${event.direction}');
}

Song Events

public override function onSongLoaded(event:SongLoadScriptEvent):Void {
  // Song chart loaded, before notes are placed
  trace('Song: ${event.songId}');
  trace('Difficulty: ${event.difficulty}');
  
  // Modify the chart
  for (note in event.notes) {
    note.time *= speedMultiplier;
  }
}

public override function onSongStart(event:ScriptEvent):Void {
  // Conductor time is now 0
  trace('Song starting!');
  startTimer();
}

public override function onSongEnd(event:ScriptEvent):Void {
  // Song finished
  trace('Song ended!');
  calculateFinalScore();
}

public override function onSongRetry(event:SongRetryEvent):Void {
  // Player restarted the song
  trace('Retrying song!');
  resetState();
}

Countdown Events

public override function onCountdownStart(event:CountdownScriptEvent):Void {
  trace('Countdown beginning!');
}

public override function onCountdownStep(event:CountdownScriptEvent):Void {
  // event.step: 0=READY, 1=SET, 2=GO, 3=GO!
  trace('Countdown step: ${event.step}');
}

public override function onCountdownEnd(event:CountdownScriptEvent):Void {
  trace('Countdown finished, song about to start!');
}

BPM-Synced Events

public override function onStepHit(event:SongTimeScriptEvent):Void {
  // Every 16th note
  if (event.step % 16 == 0) {
    trace('Every 16 steps');
  }
}

public override function onBeatHit(event:SongTimeScriptEvent):Void {
  // Every quarter note
  trace('Beat ${event.beat}');
  
  // Pulse effect every beat
  FlxG.camera.zoom += 0.015;
}

Game State Events

public override function onPause(event:PauseScriptEvent):Void {
  trace('Game paused');
  
  // Prevent pause easter egg
  event.pauseMusic = false;
  
  // Cancel the pause entirely
  // event.cancel();
}

public override function onResume(event:ScriptEvent):Void {
  trace('Game resumed');
}

public override function onGameOver(event:ScriptEvent):Void {
  trace('Player died');
  
  // Prevent game over
  // event.cancel();
}

Song Events

public override function onSongEvent(event:SongEventScriptEvent):Void {
  // Chart event triggered
  trace('Event: ${event.event.event}');
  trace('Value: ${event.event.value}');
  
  if (event.event.event == 'My Custom Event') {
    handleCustomEvent(event.event.value);
  }
}

State Management Events

Modules implement IStateChangingScriptedClass for state transition events.

public override function onStateChangeBegin(event:StateChangeScriptEvent):Void {
  trace('Changing from ${event.currentState} to ${event.targetState}');
}

public override function onStateChangeEnd(event:StateChangeScriptEvent):Void {
  trace('State change complete: ${event.targetState}');
}

public override function onSubStateOpenBegin(event:SubStateScriptEvent):Void {
  trace('Opening substate: ${event.subState}');
}

public override function onSubStateOpenEnd(event:SubStateScriptEvent):Void {
  trace('Substate opened: ${event.subState}');
}

public override function onSubStateCloseBegin(event:SubStateScriptEvent):Void {
  trace('Closing substate: ${event.subState}');
}

public override function onSubStateCloseEnd(event:SubStateScriptEvent):Void {
  trace('Substate closed: ${event.subState}');
}

public override function onFocusLost(event:FocusScriptEvent):Void {
  trace('Game lost focus');
}

public override function onFocusGained(event:FocusScriptEvent):Void {
  trace('Game regained focus');
}

UI State Events

Freeplay Events

public override function onCapsuleSelected(event:CapsuleScriptEvent):Void {
  trace('Capsule selected: ${event.capsule.songData.songName}');
}

public override function onDifficultySwitch(event:CapsuleScriptEvent):Void {
  trace('Difficulty: ${event.difficulty}');
}

public override function onSongSelected(event:CapsuleScriptEvent):Void {
  trace('Song selected!');
}

public override function onFreeplayIntroDone(event:FreeplayScriptEvent):Void {
  trace('Freeplay intro finished');
}

public override function onFreeplayOutro(event:FreeplayScriptEvent):Void {
  trace('Freeplay outro starting');
}

public override function onFreeplayClose(event:FreeplayScriptEvent):Void {
  trace('Freeplay closed');
}

Character Select Events

public override function onCharacterSelect(event:CharacterSelectScriptEvent):Void {
  trace('Character selected: ${event.character}');
}

public override function onCharacterDeselect(event:CharacterSelectScriptEvent):Void {
  trace('Character deselected');
}

public override function onCharacterConfirm(event:CharacterSelectScriptEvent):Void {
  trace('Character confirmed: ${event.character}');
}

Module Management

The ModuleHandler class manages all loaded modules.

Get Module by ID

import funkin.modding.module.ModuleHandler;

var myModule = ModuleHandler.getModule('my-module');
if (myModule != null) {
  trace('Found module: ${myModule.moduleId}');
}

Activate/Deactivate Modules

// From outside the module
ModuleHandler.activateModule('my-module');
ModuleHandler.deactivateModule('my-module');

// From inside the module
this.active = false; // Deactivate
this.active = true;  // Activate

Call Events Manually

import funkin.modding.events.ScriptEvent;
import funkin.modding.module.ModuleHandler;

var customEvent = new ScriptEvent('my-custom-event', false);
ModuleHandler.callEvent(customEvent);

Complete Example: Combo Tracker

// scripts/ComboTracker.hxc
import funkin.modding.module.Module;
import funkin.play.PlayState;
import flixel.text.FlxText;

class ComboTracker extends Module {
  var comboText:FlxText;
  var currentCombo:Int = 0;
  var highestCombo:Int = 0;
  
  public function new() {
    // Only active during gameplay, high priority
    super('combo-tracker', 100, {state: PlayState});
  }
  
  public override function onCreate(event:ScriptEvent):Void {
    trace('Combo Tracker initialized!');
  }
  
  public override function onStateChangeEnd(event:StateChangeScriptEvent):Void {
    // Create UI when entering PlayState
    if (Type.getClass(event.targetState) == PlayState) {
      createComboDisplay();
    }
  }
  
  function createComboDisplay():Void {
    comboText = new FlxText(10, 10, 0, 'Combo: 0', 24);
    comboText.setBorderStyle(OUTLINE, FlxColor.BLACK, 2);
    PlayState.instance.add(comboText);
  }
  
  public override function onNoteHit(event:HitNoteScriptEvent):Void {
    if (!event.note.mustPress) return; // Only count player notes
    
    currentCombo++;
    
    if (currentCombo > highestCombo) {
      highestCombo = currentCombo;
    }
    
    updateDisplay();
  }
  
  public override function onNoteMiss(event:NoteScriptEvent):Void {
    if (!event.note.mustPress) return;
    
    currentCombo = 0;
    updateDisplay();
  }
  
  public override function onNoteGhostMiss(event:GhostMissNoteScriptEvent):Void {
    currentCombo = 0;
    updateDisplay();
  }
  
  function updateDisplay():Void {
    if (comboText != null) {
      comboText.text = 'Combo: $currentCombo\nHighest: $highestCombo';
    }
  }
  
  public override function onSongEnd(event:ScriptEvent):Void {
    trace('Final combo: $currentCombo');
    trace('Highest combo: $highestCombo');
  }
  
  public override function onDestroy(event:ScriptEvent):Void {
    // Clean up UI
    if (comboText != null) {
      comboText.destroy();
    }
  }
}

Best Practices

Choose Appropriate Priorities

1-100: Critical mods that must run first (core gameplay changes)
100-500: UI and visual mods
500-1000: Tracking and analytics mods
1000+: Low-priority cosmetic mods

Use State Scoping

Limit modules to specific states when possible to improve performance:

// Good: Only active in PlayState
super('gameplay-mod', 1000, {state: PlayState});

// Bad: Active everywhere when only needed in PlayState
super('gameplay-mod', 1000);

Handle Null Safely

public override function onUpdate(event:UpdateScriptEvent):Void {
  if (PlayState.instance?.health != null) {
    checkHealth(PlayState.instance.health);
  }
}

Clean Up Resources

public override function onDestroy(event:ScriptEvent):Void {
  // Remove added sprites
  cleanupSprites();
  
  // Clear event listeners
  removeListeners();
  
  // Save state
  saveData();
}

IScriptedClass - Interface definitions for all events
PolymodHandler - Mod loading system
Song Events - Song event reference

Core

Audio

Play

Data

Modding

​Overview

​Creating a Module

​Basic Module Structure

​Module Parameters

​Example: State-Scoped Module

​Module Properties

​Active State

​Priority

​State Association

​Core Lifecycle Events

​onCreate

​onDestroy

​onUpdate

​onScriptEvent

​Gameplay Events

​Note Events

​Song Events

​Countdown Events

​BPM-Synced Events

​Game State Events

​Song Events

​State Management Events

​UI State Events

​Freeplay Events

​Character Select Events

​Module Management

​Get Module by ID

​Activate/Deactivate Modules

​Call Events Manually

​Complete Example: Combo Tracker

​Best Practices

​Choose Appropriate Priorities

​Use State Scoping

​Handle Null Safely

​Clean Up Resources

​Related

Build docs developers (and LLMs) love

Overview

Creating a Module

Basic Module Structure

Module Parameters

Example: State-Scoped Module

Module Properties

Active State

Priority

State Association

Core Lifecycle Events

onCreate

onDestroy

onUpdate

onScriptEvent

Gameplay Events

Note Events

Song Events

Countdown Events

BPM-Synced Events

Game State Events

Song Events

State Management Events

UI State Events

Freeplay Events

Character Select Events

Module Management

Get Module by ID

Activate/Deactivate Modules

Call Events Manually

Complete Example: Combo Tracker

Best Practices

Choose Appropriate Priorities

Use State Scoping

Handle Null Safely

Clean Up Resources

Related