JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://code.jquery.com/jquery-2.0.3.js"></script>
<script src="https://rawgithub.com/SteveSanderson/knockout.mapping/master/build/output/knockout.mapping-latest.js"></script>

JavaScript

var Klass = function(){
  this.value = 123;

  this.update = function(callback){
      var self = this;
      $.get('/', function(data) {
          $.extend(self, {value: 234});
          callback.call(undefined);
      });
  }
}
var obj = new Klass();
obj = ko.mapping.fromJS(obj);
console.log(obj.value());

obj.update(function() {
    obj = ko.mapping.fromJS(obj);
    console.log(obj.value());
});