Current

<ul id="buttongroup">
    <li>Option 1</li>
    <li>Option 2</li>
    <li>Option 3</li>
</ul>

<script>
    $("#buttongroup").kendoButtonGroup({
        select: function(e) {
            var index = this.current().index();
/* The result can be observed in the DevTools(F12) console of the browser. */
            console.log(index);
        }
    });
</script>