JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-2.0.0.js"></script>
<textarea data-bind="value: message, valueUpdate: 'afterkeydown'" rows="10"></textarea>
<br />
<span style="white-space: pre-wrap" data-bind="text: message"></span>

JavaScript

var viewModel = {
    message: ko.observable('hello, world!')
};

ko.applyBindings(viewModel);