Drawing a spiral on an HTML canvas using JavaScript

The Archimedean spiral is expressed as r=a+b(angle). Convert that into x, y coordinate, it will be expressed as x=(a+b*angle)*cos(angle), y=(a+b*angle)*sin(angle). Then you can put angle in a for loop and do something like this:

for (i=0; i< 720; i++) {
  angle = 0.1 * i;
  x=(1+angle)*Math.cos(angle);
  y=(1+angle)*Math.sin(angle);
  context.lineTo(x, y);
}

Note the above assumes a = 1 and b = 1.

Here is a jsfiddle link: http://jsfiddle.net/jingshaochen/xJc7M/