Texts

The underlying JavaScript code

    var brd = JXG.JSXGraph.initBoard('jxgbox',{boundingbox: [-1,10,7,-1], axis:false, keepaspectratio:false});

    // Vertical line at x=3
    var A = brd.create('point', [2, 5], {strokeWidth:1, dash:2, name: 'A_1'});  
    brd.create('text', [3, 8, function () { return 'X(A_1) = ' + A.X().toFixed(2); }]);

    brd.on('update', function () {
        document.getElementById('out').innerHTML = 'X(A<sub>1</sub>) = ' + A.X().toFixed(2);
    });

    <div id="out"></div>