javascript - Knockout.js binding radio group does not work -

i feel stupid can't make work :)

http://jsfiddle.net/btkmr/

i made simple fiddle prove i'm not missing in big project.

html:

<div>     preferred flavor     <div><input type="radio" name="flavorgroup" data-bind="checked: cherryon" /> cherry</div>     <div><input type="radio" name="flavorgroup" data-bind="checked: almondon" /> almond</div>     <div><input type="radio" name="flavorgroup" data-bind="checked: mgon" /> monosodium glutamate</div> </div> 

js:

var viewmodel = {     cherryon: ko.observable(true);     almondon: ko.observable(false);     mgon: ko.observable(false); };  ko.applybindings(viewmodel); 

i expect see cherry selected on start..

from knockout's documentation (http://knockoutjs.com/documentation/checked-binding.html):

for radio buttons, ko set element checked if , if parameter value equals radio button node’s value attribute.

example: http://jsfiddle.net/btkmr/2/

<div>     preferred flavor     <div><input type="radio" name="flavorgroup" value="cherry" data-bind="checked: flavor" /> cherry</div>     <div><input type="radio" name="flavorgroup" value="almond"  data-bind="checked: flavor" /> almond</div>     <div><input type="radio" name="flavorgroup" value="monosodium"  data-bind="checked: flavor" /> monosodium glutamate</div> </div>  var viewmodel = {     flavor: ko.observable("cherry") };  ko.applybindings(viewmodel);