demo-js.xml

<?xml version="1.0" encoding="UTF-8"?>
<app xmlns:fl="vs.fltk">
    <fl:window box="0,0,320,240" label="Demo Counter (JS)">
        <mixin name="+fl:button" bg.colour="#aa3300" label.colour="#99ee4f" />
        <script lang="js">
        <![CDATA[ 
        var counter = 0;

        function _update(){
            $.$('main-text').prop("label",""+counter);
        }

        function on_add(){
            counter++;
            _update();
        }

        function on_dec(){
            counter--;
            _update();
        }

        $cb(on_add);
        $cb(on_dec);
        ]]>
        </script>

        <fl:label name="main-text" label="0" label.size="90" box="20,20,280,120" />
        <fl:button label="Add" on.callback="on_add" box="20,160,80,50" />
        <fl:button label="Remove" on.callback="on_dec" box="120,160,80,50" />
        <fl:button label="Console" box="220,160,80,50">
            <script lang="js">
            <![CDATA[ 
            function callback(){
                $.log(0,"Hello world!");
            }
            ]]>
            </script>
        </fl:button>
    </fl:window>
</app>