AngularJS Example:

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<script src="//ajax.googleapis.com/ajax/libs/angularjs/1.0.2/angular.min.js"></script>
<div ng-app>
  <h2>Calculate</h2>

  <div ng-controller="TodoCtrl">
    <form>
        <li>Number 1: <input id="one" type="text" ng-model="one" value="2">  
        <li>Number 2: <input id="two" type="text" ng-model="two" value="3">
        <li>Total <input id="total" type="text" ng-model="total" value="10">       
        {{total}}
    </form>
  </div>
</div>

CoffeeScript

app = angular.module 'myapp', []
app.controller "TodoCtrl", ($scope) ->
    $scope.one = $('#one').val()
    $scope.two = $('#two').val()
    $scope.total = $('#total').val()

    $scope.$watch 'one * two', (value) ->
        $scope.total = value
angular.bootstrap document, ["myapp"]