Knockout toJSON example on root

HTML

<script src="http://knockoutjs.com/downloads/knockout-2.2.1.js"></script>
<div id="div1" data-bind="text: ko.toJSON($root)"></div>
<div id="div2" data-bind="text: ko.toJSON($root)"></div>

JavaScript

var model = (function () {
    var firstName = ko.observable("John"),
    middleName = ko.observable('2222'), //will be serialized because a value is assigned.
    lastName = ko.observableArray([1]) //won't be serialized because it has no value.
    
    return {
        firstName: firstName,
        middleName: middleName,
        lastName: lastName
    }
})();

ko.applyBindings(model, document.getElementById('div1'));

var model2 = {
    firstName: ko.observable("Bob"),
    middleName: ko.observable(""), //will be serialized because a value is assigned.
    lastName: ko.observable(null) //won't be serialized because it has no value.
}
   
ko.applyBindings(model2, document.getElementById('div2'));