Change Equation of a Graph

This example shows how you can change the equation of a graph without creating the whole construction again.

<input type="text" id="eingabe" value="Math.sin(x)*Math.cos(x)"> <input type="button" value="set" onClick="doIt()" style='margin:1em'>

  <script type="text/javascript">
   /* <![CDATA[ */

       board = JXG.JSXGraph.initBoard('jxgbox', {originX: 250, originY: 250, unitX: 40, unitY: 20});

// Axes

       b1axisx = board.createElement('axis', [[1,0], [0,0]], {});
       b1axisy = board.createElement('axis', [[0,1], [0,0]], {});

eval("function f(x){ return "+document.getElementById("eingabe").value+";}"); graph = board.createElement('curve', [function(x){ return x; }, function(x){ return f(x); }, "x", -10, 10]); //graph = eval("board.createElement('curve', [function(x){ return x; }, function(x){ return "+document.getElementById("eingabe").value+";}, 'x', -10, 10])"); //graph.curveType = "graph";

       p1 = board.createElement('glider', [graph], {style:6, name:'P'});
       g = board.algebra.D(f);
       p2 = board.createElement('point', [function() { return p1.X()+1;}, function() {return p1.Y()+board.algebra.D(graph.Y)(p1.X());}], {style:1, name:});
       l1 = board.createElement('line', [p1,p2],{});
       p3 = board.createElement('point', [function() { return p2.X();}, function() {return p1.Y();}],{style:1, name:});
       pol = board.createElement('polygon', [p1,p2,p3], {});
       t = board.createElement('text', [function(){return p1.X()+1.1;},function(){return p1.Y()+(p2.Y()-p3.Y())/2;},function(){ return "m="+(board.round(p2.Y()-p3.Y(),2));}]); 
           
       
       function doIt(){
       	eval("function f(x){ return "+document.getElementById("eingabe").value+";}");
       	graph.yterm = function(x){ return f(x); };  // usually: e.g. "x^2"

//graph.yterm = eval("function(x){ return "+document.getElementById("eingabe").value+"; };");

   		graph.Y = graph.yterm;
   		graph.updateCurve();
   		board.update();
       } 
       
 /* ]]> */
 </script>