Knockoutjs.com - Hello World Example

http://knockoutjs.com/examples/helloWorld.html

HTML

<script src="http://knockoutjs.com/downloads/knockout-3.0.0.js"></script>
<script src="https://netdna.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<div class="btn-group" data-toggle="buttons">
    <label class="btn btn-primary">
        <input type="radio" name="options" id="option1" value="1" data-bind="bsChecked: optionsValue">Option 1</label>
    <label class="btn btn-primary">
        <input type="radio" name="options" id="option2" value="2" data-bind="bsChecked: optionsValue">Option 2</label>
            <label class="btn btn-primary">
        <input type="radio" name="options" id="option3" value="3" data-bind="bsChecked: optionsValue">Option 3</label>
</div>
<br />
<span data-bind="text: optionsValue"></span>

JavaScript

ko.bindingHandlers.bsChecked = {
    init: function (element, valueAccessor, allBindingsAccessor,
    viewModel, bindingContext) {
        var value = valueAccessor();
        var newValueAccessor = function () {
            return {
                change: function () {
                    value(element.value);
                }
            }
        };
        ko.bindingHandlers.event.init(element, newValueAccessor,
        allBindingsAccessor, viewModel, bindingContext);
    },
    update: function (element, valueAccessor, allBindingsAccessor,
    viewModel, bindingContext) {
        if ($(element).val() == ko.unwrap(valueAccessor())) {
            setTimeout(function () {
           $(element).closest('.btn').button('toggle');
            }, 1);
        }
    }
}

var ViewModel = function () {
    this.optionsValue = ko.observable(2)
};

var vm = new ViewModel();
ko.applyBindings(vm);

setTimeout(function () {
    vm.optionsValue(3)
}, 2000);