ng-class example

var app = angular.module('plunker', []);

app.controller('MainCtrl', function($scope) {
  $scope.isActive = false;
  
  $scope.toggleActive = function() {
    $scope.isActive = !$scope.isActive;
  };
});

<!DOCTYPE html>
<html ng-app="plunker">

  <head>
    <meta charset="utf-8" />
    <title>AngularJS Plunker</title>
    <link data-require="bootstrap-css@3.0.3" data-semver="3.0.3" rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.0.3/css/bootstrap.min.css" />
    <script>document.write('<base href="' + document.location + '" />');</script>
    <link rel="stylesheet" href="style.css" />
    <script data-require="angular.js@1.2.x" src="http://code.angularjs.org/1.2.10/angular.js" data-semver="1.2.10"></script>
    <script src="app.js"></script>
  </head>

  <body ng-controller="MainCtrl">
    <button type="button" class="btn" ng-class="{'btn-primary':isActive,  'btn-default':!isActive}" ng-click="toggleActive()">Upload</button>
  </body>

</html>