JSFiddle - React, Tailwind, and code Playground

by wwwroot

HTML

<input data-bind="value: a" />
<br />
<input data-bind="value: b" />
<br />
<input data-bind="value: tax" />
<br />Total: <span data-bind="text: total()"></span>

JavaScript

var viewModel = function () {
    var self = this;

    self.tax = ko.observable(0);
    self.a = ko.observable(0);
    self.b = ko.observable(0);

    var sum = function () {
        return Number(self.a()) + Number(self.b());
    }

    self.total = ko.computed(function () {
        return sum() + Number(self.tax());
    });
};

ko.applyBindings(new viewModel());