SO Question

http://stackoverflow.com/questions/7373058

HTML

<select data-bind="value: val">
    <option value="1">Cat</option>
    <option value="2">Dog</option>
    <option value="3">Fish</option>
</select>

JavaScript

var viewModel = {
    val: ko.observable()
};

ko.applyBindings(viewModel);

viewModel.val(3);