Canvas work with TypeScript (image.onload now using a Lambda for scope)

gistfile1.js

/**
 * class manages drawing to a canvas
 * @author antonmills. (http://www.antonmills.com / http://www.twitter.com/antonmill)
 */
class MapController {
   
   // privates (hehe ;p)
   private _canvas;	// the render target
   private _image;	// the source image
   private _ctx;	// ctx
   private _timer;	// a simple timer

   private _startX = 0;
   private _startY = 0;
   private _counter;

   // general init, load image from string
   constructor(canvas, imagePath:string) {
		
		this._canvas = canvas;
		this._canvas.width = 960;
		this._canvas.height = 640;
		this._ctx = this._canvas.getContext('2d');

		this._image = new Image();
		this._image.onload = (() => this.imageReady(this));

		this._image.src = imagePath;
   }

   // on complete
   imageReady(p:MapController) {
		this._ctx.drawImage(this._image, 0, 0, 960, 640);
		
		this._counter = setInterval(() => this.deformTerrain(this._startX += 20, this._startY, 40), 1000);
   }

   deformTerrain(size:number, posX:number, posY:number) {
   		var g = this._ctx.createRadialGradient(posX + (size / 2), posY + (size / 2), 0, posX + (size / 2), posY + (size / 2), size);
		
		g.addColorStop(1, 'rgba(0,0,255,0)');
		g.addColorStop(0.99, 'rgba(0,0,255,1)');
		g.addColorStop(0, 'rgba(0,0,255,1)');
		
		this._ctx.fillStyle = g;
		this._ctx.globalCompositeOperation = 'xor';
		this._ctx.fillRect(posX - (size / 2), posY - (size / 2), size * 2, size * 2);
   }
}