JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-1.2.1.js"></script>
<input type="text" data-bind="value: valor, valueUpdate:'afterkeydown'">

<span data-bind="text: valor"></span>

JavaScript

var viewModel = {
    valor : ko.observable('')
}
    
ko.applyBindings(viewModel);