<p>Send me spam: <input type="checkbox" data-bind="checked: wantsSpam" /></p><div data-bind="visible: wantsSpam">    Preferred flavor of spam:    <div><input type="radio" name="flavorGroup" value="http://www.mamicode.com/cherry" data-bind="checked: spamFlavor" /> Cherry</div>    <div><input type="radio" name="flavorGroup" value="http://www.mamicode.com/almond" data-bind="checked: spamFlavor" /> Almond</div>    <div><input type="radio" name="flavorGroup" value="http://www.mamicode.com/msg" data-bind="checked: spamFlavor" /> Monosodium Glutamate</div></div> <script type="text/javascript">    var viewModel = {        wantsSpam: ko.observable(true),        spamFlavor: ko.observable("almond") // Initially selects only the Almond radio button    };         // ... then later ...    viewModel.spamFlavor("msg"); // Now only Monosodium Glutamate is checked</script>