<!doctype html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>AngularJs Demo</title>
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/2.3.0/css/bootstrap.min.css">
  <script src="//ajax.googleapis.com/ajax/libs/angularjs/1.3.0-rc.0/angular.min.js"></script>
  <script src="demo.js"></script>
</head>

<body ng-app="demo" >
  <div ng-controller="DemoController" class="container">
   <b>&nbsp;Demo</b>
    <div>
      &nbsp;Quantità: {{quantita}}
    </div>
    <br/>
    <div>
      &nbsp;<button class="btn" ng-click="incrementa()">Incrementa</button>
    </div>
  </div>
</body>

</html>
angular.module('demo', [])
  .controller('DemoController', ['$scope', function($scope) {
    $scope.quantita = 1;

    $scope.incrementa = function() {
      $scope.quantita++;
    };
  }]);