AngularJS Example

HTML

<div ng-app="">
  <div ng-controller="InvoiceCntl">
    <b>Invoice:</b>
    <br>
    <br>
    <table>
     <tr><td>Quantity</td><td>Cost</td></tr>
     <tr>
       <td><input type="integer" min="0" ng-model="qty" required id="myqty"></td>
       <td><input type="number" ng-model="cost" required ></td>
     </tr>
    </table>
    <hr>
    <b>Total:</b> {{qty * cost | currency}}
  </div>
</div>
        <button onclick="document.getElementById('myqty').value=document.getElementById('myqty').value*1+1;">Increment Qty</button>

CSS

</style> <!-- Ugly Hack due to jsFiddle issue: http://goo.gl/BUfGZ --> 
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.0.4/angular.min.js"></script>
<style>
​.ng-invalid { border: 1px solid red; }​

JavaScript

function InvoiceCntl($scope) {
  $scope.qty = 1;
  $scope.cost = 19.95;
}