EnemyStats plugin for RPGMaker MV

EnemyStats.js

/* Version 0.1.0 @kentaromiura
 TODO: remove access to 'private' properties
 TODO: find out if there's already an emitter
 TODO: text now overlaps, check how to get the Sprite height/width properties 
 for the enemy to move the text in another position
 TODO: make the text floating up and down (optional)
 TODO: add a % bar below the text (optional)
*/

/*:
 * @plugindesc Display HP of enemies
 * @author Cristian Carlesso <kentaromiura>
 *
 * @param debug
 * @desc opens chrome inspector for testing
 * @default false     
 */
!function(global){
	var parameters = PluginManager.parameters('EnemyStats');		
	if ('' +parameters.debug === 'true') require('nw.gui').Window.get().showDevTools();
	
	var slice = isNaN.call.bind([].slice);
	
	function dispatchWhenDone(fn, event){
		return function(){
			fn.apply(this, slice(arguments));
			global.dispatchEvent(new CustomEvent(event));
		};
	}

	function addBattleEvents(){
		var events = ['battleStarted', 'battleWon', 'battleEscaped'];
		['onBattleStart', 'onBattleWin', 'onBattleEscape'].forEach(function(event, i){
			$gameSystem[event] = dispatchWhenDone($gameSystem[event], events[i]);
		})
	}
	// all the $* variable get set after DataManager.createGameObjects, the plugin though runs before that call.
	DataManager.createGameObjects = dispatchWhenDone(
		DataManager.createGameObjects, 
		'gameObjectsCreated'
	);
	
	var onGameObjectsCreated = function(){
		addBattleEvents();
		// pretty sure this flag exists somewhere else
		var inBattle = false,			
			updateEnemyHP = function(){
				$gameTroop._enemies.forEach(function(enemy){
					var hpSprite = enemy._hpSprite || (enemy._hpSprite = new Sprite_Base());
					var hp = '' + enemy._hp;
					// I should get the font size and line height from the context somehow.
					hpSprite.bitmap = new Bitmap(hp.length * 32, 32);
					
					hpSprite.bitmap.drawText(hp, 0, 0, hp.length * 32, 32, 'left');
					hpSprite.x = enemy._screenX;
					hpSprite.y =  enemy._screenY - 36;
					if(hp === '0') hpSprite.hide();
					SceneManager._scene.addChild(hpSprite);
				});
				
				if (inBattle) requestAnimationFrame(updateEnemyHP);
			},
			setBattleOn = function(){
				inBattle = true;
				requestAnimationFrame(updateEnemyHP);
			},
			setBattleOff = function(){
				inBattle = false;
			};
		
		global.addEventListener('battleStarted', setBattleOn);
		['battleWon', 'battleEscaped'].forEach(function(event){
			global.addEventListener(event, setBattleOff);
		})		
	};

	global.addEventListener('gameObjectsCreated', onGameObjectsCreated);

}(Function('return this')());