Jimy,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<canvas id="canvas" width="800" height="600"></canvas>
<script>
var ctx=document.getElementById("canvas").getContext("2d");
ctx.rect(0,0,800,600);
ctx.stroke();
circle=function(x,y,radius){
ctx.beginPath();
ctx.arc(x,y,radius,0,Math.PI*2,false);
ctx.fill();
};
var ball=function(){
this.x=100;
this.y=100;
this.xSpeed=-2;
this.ySpeed=5;
this.draw=function(){
circle(this.x,this.y,20);
};
};
var b = new ball();
b.draw();
b.x = 200;
b.draw();
b.y = 200;
b.draw();
b.x = 100;
b.draw();
</script>
</body>
</html>