remove graph

HTML

<link rel="stylesheet" href="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraph.css">
<script src="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraphcore.js"></script>
<div id="jxgbox" class="jxgbox" style="width:500px; height:500px;"></div>
<button id="remove">Remove graph</button>

JavaScript

var board = JXG.JSXGraph.initBoard('jxgbox', {boundingbox: [-10, 10, 10, -10], showNavigation: false, axis: false});

var Vs = 5,
    tau = 2;
var f = board.create('plot', [Math.sin]);
var g = board.create('functiongraph', [function(x){ return Vs-Vs*Math.exp(-x/tau);}, 0, 20], {strokeWidth:'1', strokeColor:'#ff0000'});

$('#remove').on('click', function () {
    board.removeObject(f);
    board.removeObject(g);
});