Google style chart - interactive

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By clicking on points one can set new values for the y-coordinates.

JavaScript code to produce this chart

 var graph1;
 var brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-1,6,21,-1], axis: true});

function doIt() {
   var i, x1, y1;
   var p;
   var points = [];
   var x = [];
   var y = [];
   var start = 0;
   var end = 20;
   points.push(brd.createElement('point', [start,0], {visible:false, name:'', fixed:true})); 
   for (i=start;i<=end;i++) {

     // Generate random coordinates
     x1 = i;
     y1 = Math.random()*4+1;

     // Plot it
     p = brd.createElement('point', [x1,y1], 
                   {strokeWidth:2, strokeColor:'#ffffff', 
                    highlightStrokeColor:'#0077cc', fillColor:'#0077cc',  
                    highlightFillColor:'#0077cc', style:6, name:'', fixed:true}

     p.rendNode._num = i;                          // memorize the number of this point in the array
     p.rendNode.onclick = function() {
        var i = this._num;                         // Now we can access the number again
        var p = points[i+1];                       // The point number is one off
        var v = prompt("New value:", p.Y())*1.0;
        p.setPosition(JXG.COORDS_BY_USER, p.X(), v); // New coordinates for the point
        y[i] = v;                                  // New coordinates for the curve
   // Filled area. We need two additional points [start,0] and [end,0]
   points.push(brd.createElement('point', [end,0], {visible:false, name:'', fixed:true})); 
   brd.createElement('polygon',points, {withLines:false,fillColor:'#e6f2fa'});
   // Curve:
   brd.createElement('curve', [x,y], 
                 {strokeWidth:3, strokeColor:'#0077cc',