Playing with OOP JS to draw an image in HTML Canvas

HTML5 canvas ex1

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var imgs = {
    "spaceShip" : document.getElementById("space"),
    "scream" :  document.getElementById("scream")
}
function Scene(context, width, height, images){
	this.context = context;
	this.width = width;
	this.height = height;
	this.images = images;
	this.actors = [];
}

Scene.prototype.register = function(actor){
		this.actors.push(actor);	
}

Scene.prototype.unregister = function(actor){
	var i = this.actors.indexOf(actor);
	if (i >= 0) {
		this.actors.splice(i, 1);
	}
};

Scene.prototype.draw = function() {
	this.context.clearRect(0, 0, this.width, this.height);
	for (var a = this.actors, i = 0, n = a.length; i < n; i++){
		a[i].draw();
	}
}

function Actor(scene, x, y){
	this.scene = scene;
	this.x = x;
	this.y = y;
	this.actorID = ++Actor.nextID;
	scene.register(this);
}
Actor.nextID = 0;

Actor.prototype.moveTo = function(x, y){
	this.x = x;
	this.y = y;
	this.scene.draw();
};

Actor.prototype.exit = function() {
	this.scene.unregister(this);
	this.scene.draw();
};

Actor.prototype.draw = function() {
	var image = this.scene.images[this.type];
	this.scene.context.drawImage(image, this.x, this.y);
};

Actor.prototype.width = function() {
	return this.scene.images[this.type].width;
};

Actor.prototype.height = function() {
	return this.scene.images[this.type].height;
};

function Spaceship(scene, x, y) {
	Actor.call(this, scene, x, y);
	this.points = 0;
}

Spaceship.prototype = Object.create(Actor.prototype);

Spaceship.prototype.type = "spaceShip";

Spaceship.prototype.scorePoint = function() {
	this.points++;
};

Spaceship.prototype.left = function() {
	this.moveTo(Math.max(this.x - 10, 0), this.y);
};

Spaceship.prototype.right = function(){
	var maxWidth = this.scene.width - this.width();
	this.moveTo(Math.min(this.x + 10, maxWidth), this.y);
};

function Alien(scene, x, y, direction, speed, strength) {
	Actor.call(this, scene, x, y);
	this.direction = direction;
	this.speed = speed;
	this.strength = strength;
	this.damage = 0;
	this.alienID = ++Alien.nextID;
}

Alien.prototype.type = "scream";
Alien.nextID = 0; 

var scene1 = new Scene(ctx, 300, 300, imgs);
  
var spaceship1 = new Spaceship(scene1, 40, 40);
 
scene1.draw();
console.log(scene1.actors);