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This is an example of bidirectional communication of JSXGraph with other elements of the web page. a You can type a new value for the angle into the text box and see the actual value of the angle in the text box.

The underlying JavaScript code

<input type="text" id="degrees">
<button onclick="setDirection()">set direction</button>
var brd = JXG.JSXGraph.initBoard('jxgbox',{axis:true,boundingbox:[-2,1.5,2,-1.5],keepaspectratio:true});
var c = brd.create('circle',[[0,0],1]);
var p = brd.create('glider',[-1,0.5,c],{name:'drag me'}); // global variable
                  document.getElementById('degrees').value = (Math.atan2(p.Y(),p.X())*180/Math.PI).toFixed(0);
            }, 'move');

var setDirection = function() {
   var phi = 1*document.getElementById('degrees').value*Math.PI/180.0;
   var r = c.Radius();


Version 2

The underlying JavaScript code

<input type="text" id="degrees2">
<button onclick="setDirection2()">set direction</button>
var brd2 = JXG.JSXGraph.initBoard('box2',{axis:true,boundingbox:[-2,1.5,2,-1.5],keepaspectratio:true});
var p1 = brd2.create('point',[0,0], {visible:false, fixed:true});
var p2 = brd2.create('point',[1,0]);
var p3 = brd2.create('point',[0,1]);
var a = brd2.create('arc',[p1,p2,p3]);

var q = brd2.create('glider',[0.5,0.5,a],{name:'drag me'}); // global variable

                  document.getElementById('degrees2').value = (Math.atan2(q.Y(),q.X())*180/Math.PI).toFixed(0);
            }, 'move');

var setDirection2 = function() {
   var phi = 1*document.getElementById('degrees2').value*Math.PI/180.0;
   var r = a.Radius();