JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.aspnetcdn.com/ajax/knockout/knockout-2.2.1.js"></script>
<div>
    <div>
        <input type="text" data-bind="value: val1" />
        <input type="text" data-bind="value: val2" />
        <input type="text" data-bind="value: total" />
    </div>
</div>

JavaScript

function c() {
    var self = this;
    self.val1 = ko.observable();
    self.val2 = ko.observable();
    self.total = ko.computed(function () {return self.val1() + self.val2()});
}
ko.applyBindings(new c());