Draggable exponential function

Plot the function

[math]\displaystyle{ y = e^{ax} }[/math]

where the parameter [math]\displaystyle{ a }[/math] is determined by the Point [math]\displaystyle{ A=(x_A, y_A) }[/math].

That means,

[math]\displaystyle{ a = log(y_A) / x_A }[/math]

The JavaScript code

var board = JXG.JSXGraph.initBoard('box1', {boundingbox: [-5, 20, 5, -2], axis:true});

var A = board.create('point', [1, Math.exp(1)]);
var graph = board.create('functiongraph', [
         function(x) {
            var a = Math.log(A.Y()) / A.X();
            return Math.exp(a * x);
         }]);
           
var txt = board.create('text', [-3, 10, function () {
           return "a = " + (Math.log(A.Y()) / A.X()).toFixed(2);
          }], {fontSize: 16});

<input type="button" onClick="alert('a = ' + (Math.log(A.Y()) / A.X()).toFixed(2))" value="Show value of a" />