Polar curve plotter

function r(t) {return 0.2*t; };

The JavaScript code

board = JXG.JSXGraph.initBoard('jxgbox', {axis:true, boundingbox:[-5,5,5,-5]});
a = board.createElement('slider', [[0,-1],[3,-1],[-4*Math.PI,0,0]], {style:6, name:'a'});
b = board.createElement('slider', [[0,-2],[3,-2],[0,7,4*Math.PI]], {style:6, name:'b'});
function plot(){
  eval(document.getElementById("eingabe").value);
  graph = board.createElement('curve', [
            x,y, 
            function(){return a.Value();}, 
            function(){return b.Value();}
            ], 
            {strokeColor:'red', strokeWidth:2}
          );
  board.update();
} 

function clearAll() { 
  JXG.JSXGraph.freeBoard(board);
  board = JXG.JSXGraph.initBoard('jxgbox', {axis:true, originX: 250, originY: 250, unitX: 50, unitY: 50});
  a = board.createElement('slider', [[0,-1],[3,-1],[-4*Math.PI,0,0]], {style:6, name:'a'});
  b = board.createElement('slider', [[0,-2],[3,-2],[0,7,4*Math.PI]], {style:6, name:'b'});
}

plot();