JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-1.11.0.min.js"></script>
<div id="koRoot">
    
    <div data-bind="text: millionsFormatted(millions)"></div>
</div>

JavaScript

$(document).ready(function () {
    var ViewModel = {
        millions: ko.observable(1000000),
        millionsFormatted: function (obs) {
            if (typeof (obs) === 'function') return obs().toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
        }
    }
    ko.applyBindings(ViewModel, document.getElementById("koRoot"));
});