User Interaction and the HTML5 APIs - HTML5 Mastery: Semantics, Standards, and Styling - page 312

context = canvas.getContext("2d");
centerX = canvas.width/2;
centerY = canvas.height/2;
// move to the center of the canvas
context.moveTo( centerX , centerY );
// loop two thousand times, drawing a line out
further and further from the center
for (var i=0; i<2000;i++) {
degrees += 1;
radius += 0.02;
context.lineTo(
center-
X+Math.cos(degrees*Math.PI/180)*radius ,
center-
Y+Math.sin(degrees*Math.PI/180)*radius
);
}
context.stroke();
}
window.onload = init;