JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://knockoutjs.com/downloads/knockout-3.1.0.js"></script>
<button id='addButton'>item++</button>
<br/>
<span>viewModel.item = </span>
<span data-bind='text: $data.item(), bind: $data.item'></span>

JavaScript

$(document).ready(function() {
    $('#addButton').click(function() {
        viewModel.item(viewModel.item() + 1);
    });    
    var viewModel = {
        item: ko.observable(1)
    };        
    ko.bindingHandlers.bind = {
        init: function(element, valueAccessor) {
            alert('init');
        },
        update: function(element, valueAccessor) {
            ko.unwrap(valueAccessor());
            alert('update');
        } 
    };        
    ko.applyBindings(viewModel);
});