Hyperbolic spiral

It can be described in polar coordinates [math]\displaystyle{ (r, \theta) }[/math] by the equation

[math]\displaystyle{ r = \frac{a}{\theta}\, }[/math]

with a real number [math]\displaystyle{ a }[/math].

The JavaScript code to produce this picture

 var board = JXG.JSXGraph.initBoard('jxgbox', {originX: 250, originY: 250, unitX: 50, unitY: 50});
 var a = board.create('slider', [[0,5],[8,5],[0,4,30]],{name:'a'});
 var c = board.create('curve', [function(phi){return a.Value()/phi; }, [0, 0],0, 8*Math.PI],
             {curveType:'polar', strokewidth:4});